Need Fast Answers - Sitting the same A-Level with 2 exam boards...

I'm an AS student studying Biology, Chemistry, Maths and Physics who wants to do Medicine at Cambridge. My Biology and Chemistry are with AQA, whose papers I prefer and find easier to interpret. My Physics is with WJEC but my college has asked for 3-4 volunteers to sit both WJEC and AQA at AS Level to decide if they move the college onto it next year. I personally prefer AQA but would Cambridge see this as messing with the system or having an unfair advantage?
The other Universities I'm looking at are; Nottingham, Liverpool, Newcastle and Leeds.
Fast replies needed - have to let them know by tomorrow?
Thanks!