Ted,
Don't use just one "charging" pump, use as many as you need to ensure that their pump volume is at least 125% of you engine's pump at full flow. (what is the max rated flow of the main pump?) If you use multiple pumps each will need its' own inlet at the fuel tank which can actually be a large tube connected to your present -16 connection and each pump can be connected to that tube. Make it large, 2 inch would be my starting size. Run the outputs of each of the multiple pumps through a low pressure check valve, 1 psi would be perfect, then combine the flows together and run to the inlet of the engine's main pump. Just before the connection to the main pump you would need to tee in a 5 psi check valve that returns to the fuel tank, this will maintain a 5 psi head on the main pump inlet and allow extra fuel from the charge pump(s) to return to the fuel tank.
Regarding running the return line from the injection system back to the pump inlet, this could be made to work but as mentioned before there is certainly a chance of cavitation of the return fuel through the main return jet (I am assuming since it is a Blown Fuel engine you are probably running a constant flow type of injection system)which could cause the main pump to also cavitate and this type of system would become less effective as the engine consumes more fuel and the return amount become lower volume then you are back to the root problem of not enough fuel to the inlet of the pump. Pump inlet fluid velocity should not exceed 5 feet/sec and using a -16 hose that would be about 12.5 gpm which is probably less than your fuel pump, simply going to a -20 house would make the flow rate, at 5 to/sec, about 19 gpm and a -24 hose the flow rate would be about 28 gpm. This all brings up another problem that many don't consider and is a great reason to use a charge pump system, that is that there could certainly be a possibility that your -16 hose may have the potential to collapse from the vacuum created by the engine pump inlet and most of the stainless steel wire hose that we all use is not rated very high for vacuum use.
Rex