A lot depends on the actual tone of the bass, but as a starting point, assuming you already have your bass dialed in to favor the bridge pickup, I'd start with EQ nooned like in the picture.
While playing, with blend full up clockwise, bring drive up until it starts to growl and fuzz a good bit. Don't be surprised if it's above noon.
You may then want to dial back the blend to bring in more of the unaffected signal. This should smooth out the distortion somewhat and should bring in some undistorted low-end.
Depending on your strings and pickups (and default amp tone), you may need to either increase or decrease bass to taste, though Geddys tone seems to have fairly prominent mids.
Those with more experience in the Geddy department can correct me, but if you give the above a shot let me know what you think!