Hey Ben it's Ross.
I've had a look at the van versions of the berlingos and if you replace the passenger seat with a van one, they fold out of the way like so:
(http://www.rms1.co.uk/berlingo/convert/front_seat_folded.jpg)
That leaves loads of room and allows taller people to lie flat. You can either remove the rear seats or build a frame which brings the boot part level with the rear seats folded forward, it's what I plan on doing for short trips away. As mentioned above, those bootjumps have a way around it, I don't think anyone with any sense would pay 2 grand for one but you could steal the design and try and copy it.