Poop.
I think we're missing the underlying issues of restricting classes and how you would do so...
You can't. But this is the next best thing. Say you spawn in on your main and die cuz the enemy team has too many archers, then you spawn in on your cav alt and take care of them, then they spawn in on their pike alt and take care of you, then you spawn in on your archer alt and take care of them, then they spawn in on their cav alt and take care of you.
It really boils down to taking care <3 of others. I think you should be able to respawn a max of 2 times for a total of 3 lives.