I personally recommend the addon TwoBoxToolkit.

I make 5 buttons (F8-F12) on each toon, one for each of them. Sooooo...

If my Tank is F8, his button says:

/tb master 'this tank guy's name' (sets me as the new master)
/focus 'tank guy' (sets me as the focus)
/# followme (this is my chat relay channel. the other 4 should get sucked to the tank at this point. you don't have to use this follow, it could be seperate if you'd like, but i find if i've lost a toon in combat and need to switch leaders, it's nice to circle the wagons so to speak.)

Now the other 4 have this macro in their F8 slot:

/tb master 'tank dude' (sets the tank as their new master)
/focus 'tank guy'

There ya go. I also enable the Sticky Follow with twoboxtoolkit, and in Options Interface in WoW, turn on attack on assist. This way, you'll get some melee out of your 4x support as well (works nice if you use Pally/Shaman especially!) Enemy dies, and they all suck towards you, easy peasy =)