Probably the easiest way is to go into CUSTOM and select the top choice which is Custom print size. Then type in 8.1 x 10.1.
Fred

I guess I'm lost!
You want to make the prints larger for trimming?
Or do you mean you want a little larger border for trimming?
You want to end up with an actual print size of 8.1 x 10.1?

If you type in that odd size, all the images you add will be at that size.
You can set up a Layout with templates for these sizes and SAVE as a Layout.
You could add size buttons to the Print Properties size box, like 8.1 x 10/1; and 5.1 x 7.1 and so on..... Add these sizes so all you need to do is select that print size when needed.
You can even make a full set of odd sizes and save that whole set, and LOAD that set when you need them.

So many ways....

Fred

Hi Marion,
It my "work for you" but I suspect doing it that way is allowing the driver to mess up the pixels by expanding (interpolating) them. That will destroy the good work that Qimage has done in preparing the image for the printer - the fundamental reason why Qimage produces quality. 
From what you say, a set of special size buttons, probably combined with saved printer set-ups is the best answer. Again, getting the size you want easily and accuratly is another fundamental reason to use Qimage. 
Terry

ICC profiles are nothing to do with interpolation.
Qimage can use any icc printer profile whatever it's source providing it is "icc" and not some propriety thing that HP have made.
If you are printing from the driver, the interpolation from image resolution to the printer native resolution will be crude compared with Qimage's methods. 
Terry