At any given z distance from the camera the x and y distances from one edge of the screen to the other can be considered in terms of the "blitz units" they span. So if a camera-facing quad takes up the entire width of the display and is one unit wide, you know that to move it one pixel to the right you will have to shift it (1.0/horizontal resolution) units on the x axis. Operating in this manner while using as large a bunch of textures as possible is probably your best bet with B3D, although I understand that a certain amount of blurring is inevitable.
EDIT: Oh, and orthographic projection may be worth a punt.
EDIT: Oh, and orthographic projection may be worth a punt.