Haven't tried to print from LR. Might be my only other option, I still have LR 4 on here. I'm just not a big fan of LR. When I use the print option directly from other apps like Auto Pano Pro, photomatix, etc. The print dialog box that opens has 100 different paper size options but they are all std sheet sizes and no option for a 12ft long panorama. Limit on the printer isn't an issue, the only real issue is the 30k pixel limit in PSE.
I may have figured it out. Just opening in preview and printing from there. I can get to the 6400 dialog box. What I wasn't noticing was then turning on the "preview" button in the panel opens another that lets me select or add a paper size. Not quite the flexibility that's in the plugin but it looks like I should be able to print the pano.