For the record, a few years later, I've used LPG on my SEL '07 for 3 years now - and it works great. Consumption is marginally greater, power marginally lower, but all in all it's great for day to day use.
I have one in Poland.....and there's no way to use the original system in Europe. I've tried Ford in NYC, Navitech, local specialists.....and seems IMPOSSIBLE