I was working on a PM on how to do this, and decided I should probably post it up in case anyone else wants to give it a shot. I'm sure I'm doing plenty of things the hard way, but this worked for me.
DO THIS AT YOUR OWN RISK
Go get:
NiBiTor 5.6
http://www.softpedia.com/get/Tweak/Video-Tweak/NVIDIA-BIOS-Editor.shtmlnvFlash
http://www.softpedia.com/get/Tweak/Video-Tweak/nVFlash.shtmlUSB flash drive
FreeDOS usb image
http://derek.chezmarcotte.ca/wp-content/uploads/2009/08/FreeDOS-1.0-USB-Boot.img.bz2An updated bios for your card that includes the resolution you want. Your best bet may be to just get the most recent bios (or modify it using the instructions here:
http://www.insanelymac.com/forum/index.php?s=&showtopic=211294&view=findpost&p=1416376 )
I used NiBiTor 5.6 to modify the EVGA 8800GTX v10 bios.
Fire up NiBiTor
Before doing anything else read in the bios from your card, then back it up
Tools -> Read BIOS -> Select Device -> Pick your card.
Then Tools -> Read BIOS -> Read into File... And save it someplace safe. Then make a backup copy
Now, Tools -> Read BIOS -> Read into NiBiTor and we can start looking at your bios info.
After this, open a second copy of NiBiTor to edit the donor bios. Go to the Adv. Info and match your Sub Vendor ID, Sub System ID, and Board ID. Your Device ID should probably already match. There might be something wrong if it doesn't.
I went through the tabs and matched up the clock speeds as well (I only matched my clock speeds because I had and OC edition card - most cards would ship with stock speeds so you probably won't need to modify these).
I also went to the Boot Settings tab and unchecked the Display Boot Messages box because I was tired of seeing this before my mobo bios. This is optional (obviously).
One note: Just above the tabs in NiBiTor, you'll see your Product: info. My stock bios says G80 Board - 0355h00, the bios I flashed with says G80 Board - 0355h05. I had no problems, but this worried me more than anything else. Lesson learned; it's at least ok for these to not match up sometimes.
Once you're done modifying the bios, unzip the FreeDOS image, then dd it onto your usb key (it will erase everything you have on your key)
SAMPLE dd command from OS X (modify for your actual file location and your disk):
sudo dd if=FreeDOS-1.0-USB-Boot.img of=/dev/disk10 bs=4096
Now mount your USB key (OS X does this for you) and drag in your modified bios (and a backup of the original in case something goes wrong).
Also copy over the nvFlash utility.
Now reboot and boot from the FreeDOS disk. use
nvflash newbios.rom
to flash your bios. If there's some mismatch, you may need to use
nvflash -4 -5 -6 newbios.rom
to force the flash (I had to force the flash).
Edit: Added a couple more code tags for easier reading