A Workaround for the Centering Issue?

In my 25 October posting I mentioned a centering issue. In a nutshell, when I print these profile evaluation images, which are 7.5" high X 10" wide, on letter size sheets, with the "Center image" option checked in the printer driver, I get top and bottom margins of exactly .5", just as I expect. But the left margin is .25", while the right margin is .75". The image is quite clearly not centered.

For most of my own work that will be matted (whether framed or not), I mostly don't care. But I think handing a client a contract-printed piece that's off-center on the sheet will look amateurish, at best, and if I cut the right edge down so the image IS centered, the sheet is no longer the size I advertise, and on which I base my prices.
Also, I have one "special" print I do that requires pretty precise positioning on the page. I print two pictures on a 13x19 sheet. They have .5" borders on all sides. I need those .5" borders! I put 1" between the pictures, so when I cut them apart I have half-inch borders on that side, too. With the iPF 5000, I'd make a new file that's 18" wide x 12" high (or vice versa) at appropriate resolution. Each picture would be optimized the way I'd want, flattened, pasted into the new document as a layer, and then positioned so it's 1" from the other picture. When printing, I'd choose 13x19 sheet, check the box to center the image on the page, and print. It would come out with perfect 1/2" borders on the four sides. (This doesn't provide a lot of area for hinge mounting, but it's worked fine so far. I use acrylic self-adhesive "conservation corner mounts" on the bottom two corners for additional security.) I've been framing these with Larson-Juhl Digital White mats and Nielsen "standard" frames in graphite. This makes a very nice looking picture that's clearly larger than one can make on a "kitchen-table" printer, doesn't cost a lot to produce, and sells at a reasonable profit. Honestly, I don't know if I can do this with the Epson. I can certainly print one such picture on a sheet, let the Epson print it off-center, and frame it as usual (after cutting down the sheet a little). Doing that doubles my paper cost for these pictures, but if I have to live with that I can. It's about time to raise my price for these 10% or so anyway!

Those are my reasons for being more than a little unhappy that the Epson has this "feature". It just seems ridiculous. I dug around on Luminous Landscape's "Printers, Papers, and Inks" forum and found one other post, from 2009, I think, in which the OP complained about this and asked for help. The consensus was, most users don't care, don't really object to this. I find that pretty amazing, too.

I tried a test in which I created a custom paper size, which is done in the printer driver. This custom size is 8.5" X 11", but has a top margin of .25", with the remaining three margins set to 0.00". When I save this, complete my page set-up in the driver, and then save (which returns to the main printer driver window), the dimensions shown under the "Center image" checkbox are Top: 0.5", Left: 0.375". The preview image shows the entire sheet shifted slightly to the left. When I make the print, the resulting left margin is just slightly under 1/2", while the right margin is about 9/16". Still not quite centered, but I think this is as good as it gets. With these settings the image is dangerously close to being clipped on the right.

  --Jay