Their is a guy on here, I think he goes by bikebuilder who uses the dual intake. He has a cabling system that has the second carb. kick in like manual secondaries on a old holly. I could be wrong on this but this seems like it would be better as the little tiny motor wouldn't have to make up for so much intake volume till it had enough rpm to do so.
That was my thinking. Either that or go with two extremely small carbs so both small carbs equal to the volume of say a VM18mm carb for example. Either that or design a bell crank that as you said would start to pull on the second carb around 1/2 throttle but have its pull ratio set up to pull wide open throttle in half the distance that the other carb does.