From the PSP specs that I've seen in a few places, it says that the PSP has 4MB of EDRAM instead of specifically saying that there are 2MB of vram for the GPU, and 2MB of EDRAM for the ME. Are the vram and edram on the same chip, and just partitioned like the PSP Slim's memory? In that case, could the firmware unparition it so that there was 4MBs of vram? Just a thought, and I'm sure if my assumptions were true, this would have already been discovered and done ages ago.
Could the edram from the ME be patched or something in the application's software (and not the firmware itself) so that edram could be used as vram? I've heard talk of allowing the ME to have access to the main memory, so that maybe it would be possible to do the reverse of that.