printing in odd size

[Giedo]

Hi,

Im currently printing a Moab Chinle digital book. Book and paper (entrada, 190 grs, natural) look very nice and due to a custom profile, the prints look great.
There is only one thing: I want to print borderless or at least as big as possible on this paper, which is 8 by 8 inch.
My printer (Canon i9100) however, does not recognize 8 * 8 inch.
So what I do now is rescaling from A 4 to a custom size. But this is complicated, resulting in a lot of misprints on expensive paper. And I cannot print borderless...
Does anyone know a simpler way of printing from photoshop to this odd size?

Thx,
Giedo