overdriving t8's

So I'm wiring up a old 4 bulb T8 fixture for some mothers and i want to overdrive them on occasion, not all the time, probably just a week or so before taking cuts. Most of the wiring i see to overdrive has a 4 bulb ballast driving 2 bulbs. What I want to do is wire the ballasts in parallel, so that one ballast powers all 4 bulbs, then when i hit the switch, the second ballast will start to overdrive them. any reason I can't do this? I don't see any. Or would i be better off overdriving two bulbs constantly, and having the other 2 on a switch? I'm also going to wire a old 120V muffin fan in for some cooling...anyone know if they can be put on a dimmer or what style can be?

Hopefully someone can chime in soon..i'm about to go play with my lights..see what i can do..