I think some sort of piggyback is in order. 20v ecu's seem to run a bit rich at higher rpms, but I doubt that will accomodate a turbo. The other thing is that there would be no way to adjust spark without a piggyback at least, so thats another problem.
Of course you could always go full standalone. I can make adapters that would make a standalone a direct plug-in proposition.
Here's a haltech that might actually go for a cheap price:
http://cgi.ebay.com/ebaymotors/halte...spagenameZWDVW
And of course there is megasquirt2. I may have worked out a way around MS's problem with the 20v cam trigger.