For future reference, I found that a good time to create the partition was during formatting with WinHIIP (if one goes that route). I made a 4GB +OPL partition at that point, and then it's always at the front of the disk, before any HDL or other partitions are even created.
Chip-free/MC-free homebrew <3
FMCB 1.93 on MC for emergencies, NA
250GB HDD/FHDB 1.93/OPL 0.9.2 (GSM and non-GSM)/PS2 games, NO HDDOSD
80GB HDD/FHDB 1.93/POPStarter rev12/OPL644/GSM0.37/PS1 games, NO HDDOSD
SCPH-75001 (sitting idle, slims suck):
FMCB 1.92 on MC