So far, I've found a couple of things of interest

You can access the extra filter modes:
CC No. 68
Notch 24dB (Data 7)
Notch 12dB (Data 8)
Comb+ (Data 9)
Comb- (Data 10)
PPG VCF (Data 11)
You can also put the Sledge into Unison Mode:
CC No. 99
Poly Mode - No Unison - as on front panel (Data 0)
Mono Mode - No Unison - as on front panel (Data 2)
Poly Unison - Uses 2 Voices (Data 16)
Poly Unison - Uses 3 Voices (Data 32)
Poly Unison - Uses 4 Voices (Data 48)
Poly Unison - Uses 5 Voices (Data 60)
Mono Full Unison (Data 127)
Unfortunately there is no Unison Detune… But you can set LFO 1, 2 or the Mod Wheel to a slow Sine or Triangle and add a touch of depth to detune.
That's all I've come across at the moment, but I'm looking into the SYSEX side of things…