There is a "cheap" means of DATA "bank switching" which you may be able to apply since 64k of code should be plenty for your purposes. What you can do is things like:
void(write_display_page_buffer(void)
{
//disable interrupts
//set page n address (16-23) in P1
do the stuff
// clear p1
// enable interrupts
}

This, of course require that you are not depending on fast interrupt responses, but it does not seem you do.

Erik