And Ego and an A5 are not comparible, unfortunately. But the info will be helpful for others who search it.
You're running into the same issue all MilSim guys do; how to get rid of the tank, but still get a decent number of shots. Short answer is you cant. You can use 9oz tanks and carry a spare. They're very small;
20, 12 & 9 oz
Or run a remote. Those are the two best options if your tank is in your way.