John, I am sorry you did not appear to get what you wanted from Hasselblad UK. But I am a bit confused, the GPS power consumption (as far as I know) draws very little power, it is a very small solid state device, and I don't recall this being an issue with anyone else, also I think you are based in Italy so how did UK get involved?
Please supply more info here or call direct.
One thing I suggest to all my customers is a simple powered firewire buffer, remember that Macs (used to ) provide 10 Watts so aim for that.