There is a way, but I wouldn't recommend it.
The hack needs to tricker to run unsigned code. Therefore the update.xbe need to load to tricker the hacked fonts and pbl. If you get one of the first versions of Rmenhals fonts they dont check for an unset clock. Therefore if you were to let your xbox loose time by leaving it unplugged, the retail bios would always try to boot C:\xboxdash.xbe (which is the update.xbe) on boot. This would tricker the fonts and thereafter PBL. If the bios that PBL loads checks for a D:\default.xbe (most bioses do), the backup would boot.
The danger is that if you files on the HDD or the HDD itself get corrupted somehow, you wouldn't even be able to boot a retail game this way.
An alternative was to modify the existing fonts for check for D:\habibi_default.xbe before PBL is loaded. That would mean that you would have to add an habibi signed default.xbe to the backup before burning it, and habibi sign every other xbe,xip that the game uses.
I would say it's worth waiting the 5 secs. it takes to load PBL
