I wrote an email few hours ago, and as no fast response given I decided to
try to implement by myself.
I got it, (or it seems), I am able to write to page > 0 in graphics mode.
I attach you the patch to compile under OpenBSD and also write on page > 0
Also I attach the raw image (that only works on QEMU not BOCHS).
But you can compile it if you want:
P.D: master branch is painting pixels very slow. The SeaBIOS of qemu
package in OpenBSD is painting really faster.