Yellow van with square wheels for you me thinks john[]
However, I do believe it is possible[]
but.............. better on normally aspirated fuel injection vehicles rather than turbo's from what i've heard/ read.
As Stephen says its not a mapping issue but a whole new set up with tank in the spare wheel well, additional "ugly" filler cap and feeder pipes etc.etc.. youd be looking @ £2k+ for the setup which would take a while to recoup unless your planning on keeping your car for a good 2 years+.
Looked into it before when I had the Forester Turbo and decided it was a HUGE expense (outlay) for a long wait for your candy back.
Gus