what we used to do was if a person signed up with say a dps char and his healer was needed, we had a raid start time of xxx and everyone needed to be online and at the raid startup place 10 mins before, the raid leader could in those 10 mins say to them the healer is needed so they could swap chars and because everyone was there ready, a summon by the summon stone was quick and not much time wasted in waiting for him to swap chars and make his way there.

They way I'd like to see this is...

When you "Approve" someone for an event, it gives a flyout next to Approved that shows all their toons.

So they may sign up with their Warlock but I approve their Druid (Healing).

Or something like that.