On a boat motor, those bulbs are meant to be on the suction side. You want to pressurize it with fuel coming out of the mechanical pump? On the suction side, if there's any obstruction downstream the bulb will get sucked shut and you will run out of fuel. They work great on 2-strokes with their super low pressure fuel systems, however even there they can cause issues. I don't think it would work well long term but it would be a neat experiment. If you put a T in a the fuel line with shut-offs, a second fuel line going to your tank it would work.

If you've ever installed an electric fuel pump you will never go back. I put one on every carbed car I own. All I do is put the key in the run position, leave it there for 5 seconds or so while the fuel pump refills the bowls, pump the carb and start like normal. Even after sitting 6 months they fire up like nothing. A buddy of mine liked mine so much he put one on his school bus-camper that always used to take years of cranking now fires up easy. Other than a resto project I wouldn't mess with a mechanical fuel pump again.