i have the same problem with my Canon i9900. I emailed Canon and the reason they gave me was because the ability was not included in their software (as you alluded to with Epson's software).
I assumed that one would be able to do borderless 12X12 printing with Epson since Epson makes 12 X 12 Scrapbook paper. However, if you read that paper box carefully the size of the paper is 11.46 (or something like that), not really 12. When I used 11.46 as the size of the paper, that was the closest that I came to borderless printing.
I don't mind so much though, as I have now got in the habit of cutting the trim off with a paper trimmer (I think the brand name is Carl) that allows for up to 11 different shaped blades.
On another link someone mentioned getting true 12X12 borderless printing at a place called
http://www.ezprints.com/
for about $4.70 or so each. I plan to give them a try if there is ever a situation where I feel I really need it. The person who mentioned them on the link, stated that the prints were of high quality.
BTW I am still happy with the purchase of my Canon i9900.
