What I did to minimise the difference in hardware between bootcamp and PD (3 at least, seems ok in 4 too) is to make sure the MAC address of the Virtual Network Card is the same as the MAC address of the physical network card.
This is one of the triggers, and doing that meant switching between Parallels and Boot Camp didn't trigger the "your hardware has changed too much" thing.
Last night, upgrading to PD4 tripped up the Windows Activation wizard. I tried to do it online, and it said "you'll have to call by phone because you've made too many changes". When I set the PD4 network card MAC address to be the same as the physical MAC address, it let me activate online (I think because the hardware was similar enough my PD3 setup to fly under the radar).
If you are doing a fresh install, definately do what did. If you are upgrading PD3 -> PD4, it is probably less important that the virtual MAC address match the hardware and more important that it matches the PD3 setup (so hardware change triggers are minimised).
Let us know how you go.