Open Manager 2.1-I has an option that allows for game data to be installed on an external HDD instead of the internal HDD. It still works for 3.55 users but hasn't been updated to add lv2 patching for games so you would need to be running Waninkoko's CFW (or a MFW like mine with lv2 patching) or Kmeaws lv2 patcher every time to be able to use the manager and load games.
PS3 CECH-2501A [CFW] & CECH-3001 [OFW]/ PS2 SCPH-3901 & SCPH-7501/ PS1 SCPH-5501
Mod Cobra 4.46 v7.00 w/ E3 Flasher [CFW] & Cobra ODE 4.50 [OFW]/ Mod HDD-OSD [Phat] & Modbo 4.0 [Slim]/ Mod MM3
HDD 1tb [CFW] & 640gb [OFW]/ HDD 640gb & OPL v0.92 w/ 1.5tb SMB