I setup PowerAuras on my slaves with a HUGE icon for the injection so it was really really easy to see which toon got it. As Fur suggests - Click to Move and just getting away from everyone else ASAP is the way to go.

This and the Thaddius fights really forced me to step up my multi-toon awareness.

random suggestions:
Can you take over tanking the boss and have the other tank pickup adds? Then you only have to worry about walking him around the circle
set your alts /assist to another DPS toon in teh raid and work with them to ensure that the right target is getting burned