Thanks for everyone's feedback so far; indeed, upon further investigation it appears that borderless printing is indeed only possible on the top and bottom of roll fed paper - not for cut sheets.
In my original post, I mentioned A4 as being able to be printed 'borderless', due to the 'borderless' check box becoming available when A4 paper was selected in the Epson print driver.
Upon further inspection of the printer, it looks unlikely that feeding regular cut sheets into the printer will work with borderless printing on the top and bottom of the page; the sides seem to be fine but not those two edges.
I have looked around for 11" wide paper rolls of reputable quality (I really like Red River, but they don't offer them in anything but 17" and 24" wide), but have yet to find any that meet the bill. Does anyone have any recommendations for other paper suppliers who might stock or be able to provide 11" wide rolls?
I really, really do not want to have to guillotine cut countless 17" roll sheets into two 8.5" wide prints over and over just to get a simple borderless print going...
Alternatively, does anyone have a suggestion for a companion Epson printer I could get to run mass letter-sized prints through?
Thanks