No. You can't use any homebrew on 4.0 So now the games will always be stuck in the system unless he can "somehow" downgrade back or reformat the entire system. He should have took his time and transfired his games back to his computer or backed them up to another hdd of some kind before updating.
He knows nothing about this stuff. I synced his trophies for him so i guess the only other thing to do would be transfer his saved games to a usb hard drive before i replace his hard drive? Take out the 500gb and put back his original 80gb.
The best way (Unless 4.0 has a FULL format option) is to backup gamesaves, and anything else he wants to USB. Then pull out the HDD from the ps3, and format it to fat32 or NTFS via USB enclosure etc via laptop... Then put it back into the ps3, and it will ask you to reformat the HDD and reinstall 4.0 Firmware (You will need the 4.0 firmware downloaded to a USB stick). And you will be back to a fresh 4.0 Ps3
Someone correct me if I am wrong... Backup the savegames. Then you can take out the 500gb, put into an enclosure and use your pc to format it. Put it back into the PS3 and let the PS3 do its work. Then you won't have to put the 80gb back.
After the PS3 did its job, restore the savegames. Some savegames might not work after restore because it was saved with a jailbreaked system. Hope this helps.