I can't see you having too much of a
problem mounting 4 ballasts... it's what I'm planning on doing!
That said , it might be a little more tricky if you're planning on keeping it all looking OEM.
I've currently got one ballast stuck to the washer bottle, and the other stuck to the body panel right next to the airbox (both using that 3M Dual Lock heavy duty velcro stuff).
Planning on sticking the second drivers side ballast to the other side of the washer bottle, and the second passenger side one underneath the slam panel for the headlight (like UncleFester). It might not look brilliant, but it should do the job just fine. Besides which, they're easy enough to remove and relocate if I decide I want to start entering shows!
Just pop your bonnet and have a look round the engine bay - you're sure to find plenty of locations.