there are such things as multiple emitter transistors. Used to use them in digital OR gates. If it really was a multiple emitter transistor, I would hook up the unwanted emitters to a bias source so that they were cut off, in other words, it the base bias was 1 volt DC, I would make the emitters anywhere from 0.4 volts below that to maybe 2 volts above that. That way they are not conducting, have no charges in them, and therefore present a minimum capacitance. Just remember the reverse breakdown voltage of a base/emitter junction is very low...especially for microwave transistors, so use a current limiting resistor if there is any chance of a reverse breakdown.