I don't know Tool's bassist well but in the late 90s I was chasing Geddy's Wal sound and I've actually thought about doing this mod to a T-40 as it should give a nifty sound difference and lighten the bass.
If you rout out a 3rd pickup cavity in the middle where the Wal's pickup is, you could probably get someone like Buzzardsbass.com to make you a guard with the pickup moved back. Basically a 50$ mod that gets you at least a placebo.