None of the "standard" ELFs are actually required to be installed to the MC to boot FMCB, if you want you can keep them all on a USB drive and run them from there. I do always recommend at least putting uLE on the MC, as it's very handy and would be always usable even if something happened to your USB drive suddenly. uLE 4.42a is only 440KB as found in the install packages.
Chip-free homebrew <3
SCPH-39001, FMCB 1.8c, NA+250GB HDD
SCPH-75001, FMCB 1.8c
GSM 0.36 + OPL r639 = Gaming bliss ^_^