Or you could do it the easy way and use a carby manifold with EFI Hardware throttle bodies or similar. The 20v throttle bodies are also easily fitted to the carby manifold using adaptor plates but then you need to adapt a fuel rail and fit injector bosses to suit into the manifold.
It is actually possible to retain a standard ecu but I wouldn't recomend it. Obviously the whole idea of fitting quad throttles is to improve performance so you'd be best off doing it properly and using an aftermarket ECU.
As an aside though all of this would be a waste of time and money if you are running a stock or near stock engine. Without a reasonable amount of work done you would get very little benefit from the added air flow into the engine.