Though i have recent retired from multiboxing, i keep an eye on the forums.
My 5 man group consisting of prot warrior, 2 fire mages, shadow priest, holy pally used the sheep macros all the time. Similar to the post above, button one would set the raid targer on the main while the mage would /assist the tank and set his target as their focus. The second mage would do the same thing but on another button. Then a simple /cast polymorph [target=focus] set to button 3. Having them /tar focus and /say Targeting %T to sheep will help identify if they are on the correct target. Sometimes if you try to set them too quick, one of the mages will say Targeting <no target> to sheep, stop, and reset him. This is also nice for resheeping mid fight. Of coarse this will only work if you macro system is setup by /assist tank /cast spell.
Hope it's not too complicated.
ForThe Horde!
Pure Hairy