Mr. Backup Z64 FAQ

Mark the game that needs a boot emulation in the list of the on screen menu and press c-left.
Then choose "Detect Boot Chip". Quit the menu with B and save with A.
Your boot cart should be one with a 7101/6102 chip like Mario.

As an alternative you could just use the right boot cart with the same CIC as the game you want to play.

In the same menu you can enable the country fix, so you can play a PAL game on a NTSC console.