First off tell him he doesn't need that many points into Prot to offtank.
When my toon was fury (17/44/0) i still successfully offtanked one of the elites during the Moroes fight. When it comes to off tanking it isn't the spec that makes the difference it's the gear.
I can't say much about good MTing as i think i'm not that great as an MT,
but i can give advice on off tanking.
As soon as u got 5 sunders on the mob do a sunder every 3-4 seconds, hit Shield block whenever it's up and do the same for revenge.
If he does go MT, tell him not to pick up Imp. Revenge.
some people might not agree with my reasoning, but i find the best way of tanking is to be taking a beating to make ur rage generate faster which means more devestates/sunders/revenges/HS. Imp. revenge will stun ur mob giving you less rage. Only time it's useful is if ur tanking 3-4 mobs at once so u can take one of the the picture for a few seconds to give the healer a break.
Spec It may not be the best spec in the world, i'll admit cause it's been a while since i seriously thought about a proper tanking spec. but that one will do a good job. the anger management will help with rage generation