I've got a BGE, and do what you are describing. The positive lead from the battery is just below the fuel pump. You can push aside the rubber boot covering the bolt on the positive lead. Then separate the flat spade connector on the fuel pump wire, then touch the fuel pump side of this wire to the positive lead from the battery.
The pump will start, let it run until the pump slows, this will let you know the carb bowl is full.
I've thought about wiring a primer circuit, by installing a momentary switch from the battery lead to the pump connector (fused), but was concerned backfeeding the fuel pump circuit would cause issues. If you try it, let me know if it works...
Jim