you can
Go to Applications folder
Right click on Final Cut Pro & choose Show Package Contents
Double click on Contents folder
Open up info.plist with TextEdit
Search for AGP and replace it with PCI
Save
im sure it works i did it a while back but that may have been with 4.5 but thankfully my uni technitions where kind enough to lend me final cut pro 5.1 anyway it may save you a few bob if it works😎