Scale a window?

I have a program that can only run at 800x600.
I'd like to run it in a window but at 1.5 scale.

Xephyr -> x11vnc -> tightvnc has gotten close but is too laggy, kmag actually seems to work the best for this purpose but the rescale method doesn't look very good.

I would've imagined there is some sort of way to grab an x11 display and upscale it but I can't find such a program.

Anyone got any ideas?