This is not for production work, but if you want the occasional 16x24 or larger it might do. You have to have space to do this. Making the rig takes a little time but cutting the paper is pretty fast and accurate.
First I made my own D roller (search forum). It did not work on 17x36 (pano) paper very well. It flattened it pretty good except for the very ends which still had a slight curl at the ends, no problem for mounting only printing. This hit the heads about the last inch or two and left black ink smudges. The cure here would be to cut the paper to 16x40 or so the smudges fall outside the wanted paper size and trim.
Now to 16x24. I use a Epson 3800 so no roll paper on the machine. Assuming you are using something similar in 17 inch width the trick is to think laterally. Instead of trying to print the 16x24 on 17 inch paper with the 24 inch dimension coming from the length of the roll, use a roll of 24 inch paper and get the 24 inch dimension from the width. Cut off a length of the roll a little longer than 3 or so sheets. Flatten that as best you can with your roller. Then cut this sheet down to the 16x24.
I use a homemade cutting board, see quick image, no quite finished yet. It is a 2x4 foot piece of MDF. At one end is another board with the cores from the roll paper screwed down to hold the paper. I used the cutting bar from my mat cutter and pin registered it so that it is perpendicular to a yard stick and that is perpendicular to the paper roll. The bar slips over two pins and up against two wood block so that it is firmly held in place and allows a good cut. In place of the mat cutter bar you could fashion something similar out of stock aluminum bar. Placing the edge of the paper against the yard stick assures a perpendicular cut and makes easy measurement.
I am using 17 inch roll paper but think I might scale up my board for 24 inch. Instead of 2x4 ft MDF make a 3x4 ft surface from a larger sheet. ( 2x4 ft is a stock size. You can buy a larger sheet and Home Depot, etc. will cut it to size for you).
This works because the 24 inch width has no curl. The slight curl is now along the other dimension and does not effect the printing.
A lot of work and may not be worth it. It is low tech and low cost and if you have more time than money may be worth a shot. Works for me and I can now print all those odd sizes, 8x14 etc., since I crop for image impact not paper size and use lots of simple panos.
