Apparently the way they do it is to tap into each of the runners (between the butterfly and the head) and run them into a single line which then feeds the sensor to get a decent signal. I've heard that you don't get enough of a reading or something if you just try to get it off one of the throttles.
It's been done HEAPS of times in clubbies. most clubbies built since around 2000 run the 20V silvertop and a fair proportion of those now run aftermarket ECU's. Try contacting the PRB distributor in your stateand ask them. All of their 20V's run MOTEC and read off a MAP sensor.