I knew someone who had Mk1 Vito diesel with lpg injection, though his had never worked whilst he'd had it.
You can, of course, convert a diesel into an lpg engine, but it will never run on diesel again; not for the feint hearted- requires remachining the head to convert injector ports to take spark plugs, reducing the comp ratio by machining the piston crowns and adding a spacer plate etc, as well as fitting an aftermarket lpg kit.
I have a friend who had done this to a London Taxi (with a 2.7 Nissan engine) and found it excellent.
However the PD injectors and OHC make doing this impractical to a T5.
It was also regularly done as OE when lorry engines were converted for fork truck use.
Tuffnels run some of there trucks on diesel with LPG .they did trails for it ,its supposed to reduce emissions and running cost.
But didn't work well .think they run 80% diesel and 20% LPG or something like that