Should just have to resize (to keep v and h the same size) then once your run your seamless tile, you can then resize either the h or the v to get the perspective that you find necessary. As a sample of Simple's Diamonds in action, I released the two tiles on my Deviant that uses this filter; both are seamless). Just click on the image for their Deviants.

0 deg:

45 deg (Used Simple for this one. I actual first increase the 0 deg size, ran simple, then decreased it back to the original to keep the perspective size the same as the 0 deg one):
