Need Help in getting Aura-Emitters to stay put

[tinkthank]

This could be applicable to any nation, but I'll make this specific for my specific problem:
Tien Chi S&A, early game: Get the Iron Crutch around turn 4. I'd like to send him out with my expansion team because he can schlepp those summoned Spirits with him and is a good searcher, also immortal in case things go wrong.
However....
I put him all the way off to the right rear of the field and tell him to cast spells. But he then runs right behind my archers and diseases all my troops and my commanders, who are also behind the archers (rearish left).
I tell him to cast specific spells (air shield, twist fate), but since he cant really cast much else(I am reasearching construction), he has nothing to do and so runs out (pretty fast for a crippled old man, really) and diseases my troops again.
I give him some bodyguards (dispossed spirits, immune to disease), but he still wont "stay behind" them. He then runs with them into the armpits of my displeased Noble, who is obviously too polite to tell him to piss off and go disease someone else.
Now I successfully conquered a few provinces, but my prophet, commander, and half my archers are diseased.
Is there any way to get him (and similar unhealthy-aura emitting units) to keep away from the rest of the troops? Must I tell him to attack? But then I dont want him diseasing my front line troops either....
what can I do (besides: keep him out of battle until he learns some ranged spells)?
thanks much in advance