THE CONCLUSION..... IT HAS WORKED, IT WAS DONE IN LIGHTROOM.
Despite the advise here, I was unable to get a print with Qimage, maybe I needed to spend more time with it. I have written the whole story here:
It started a bit like this like this "You know that large printer of yours, do you reckon it will print a large cartoon, like really large?". "Sure, why not" I say, "it's got a roll function". We were up to midnight that night with no luck from the Epson 4900.
Before I get too much further, you'll want to know more about the print. It is a long cartoon with pixel dimensions of 2,550 x 94,488, or approximately 17 inches wide x 52 feet (16 metres) long, at 150dpi. At the moment, you can also view it here in 20 sections. http://www.nicartoons.com/ottimeline/?id=1
Firstly I'll start with what did not work. If you only want to know what did work, skip this section.
The paper came from office works that afternoon, it was the only place open, but they didn't have 17" roll paper, every size but 17". The closest was a 15" brown craft paper, usually I wrap packages with it. It's very thin, and the core size is only 1 inch, the Epson needs 2 or 3 inch, so we figured it could be sheet fed.
Mistake number 1. This paper is very thin so feeding it into the sheet feeder was very difficult, and needed to be pushed in with a thicker piece. 2. When it did feed through it tended to get caught up inside the printer causing a very worrying paper jam at one stage (it got caught up by curling up inside and not coming out the correct slot). 3. Trying to hand hold a roll of paper and control the exiting paper at the same time, not so easy.
Learning: Do not try to hand feed a large roll. Do not try to print with very thin paper.
Next. The software issues.
Printing from photoshop.
First attempt was to print from photoshop. We set up a custom paper size of about 15" by 45 feet or so, which was large enough to print the whole image. Hit print. Wait. Nothing. Try again, nope. I can't say what happened but it just would not print in photoshop. Lets try some other software.
Printing from Lightroom.
First hickup, lightroom will only import files smaller than 65,000px, so after realising this we decided to chop the image up into 10 separate files, this was done back in photoshop within a few minutes. Images imported, go to print module. In lightroom we tried a similar method to photoshop, used a page size of about 15" x 45feet, but this time set the page layout so that each image was aligned under the other, giving the impression of a continuous image. This is done with the margins, cell spacing and cell size options. It was looking good, hit print, got a print preview and it started. Cheers all round, we were happy.... for a couple of metres. After a short while the print just stopped. It was about midnight. Time to give up. This limitation was most likely imposed by the print driver. The epson driver is limited to 32,767 px, which is 91 inches long (2.31 metres) at 360dpi.
Printing from Qimage.
This was a new day, and we had new paper, proper roll paper 17" wide and loaded in the Epson 4900 roll feeder. I really thought this would work. Prior to attempting this, I had installed the demo version of Qimage, and had exactly zero experience with the program. So thinking it would work it's magic, I set a large paper size, roll paper, correct alignment, hit print. We see the message "processing", it's taking a while, lets go have dinner. Half an hour later "processing". So I can't say what went wrong here, but I had another idea.
What did work!
Lightroom attempt number two.
So, if you can only print 32,000 pixels on a page, what about printing multiple pages onto roll paper, but with no gaps in between? It worked. So we imported the multiple sections of image as separate images. Head to the print module and create a paper size of 17" wide by 54" long. This is long enough for the image to fill the page when extended to the top and bottom edges. By setting lightroom to zero spacing, zero margins, and a cell spacing height of 54" the image stretched from top to bottom.
The printer was then set to roll paper (borderless), plain paper, black (ink).
It was looking OK. Hold breath and HIT PRINT.
There was a good reason to tick the print preview box, it showed 10 separate images, each one printing right to the edge. The printer spooled up, and off it went, about 10 minutes later we were looking at a 15 metre long cartoon, happy days!
Despite the size, this print surprisingly only used 3.5ml of ink, it was set to black which may have helped, and being a cartoon most of the picture is white.
One warning though, before printing a large colour panorama photo on expensive paper with this method, I would want to check very precisely if there are any visible lines at the page borders, As we printed it all looked seamless, except perhaps for one single, very fine white line / gap. It was almost indistinguishable and did not matter for a cartoon, but we didn't spend the time to work out what caused this, on an expensive print I would test the method a bit more prior to printing.
I attached a picture of Nick, happy with the result.