I'm not sure if you would want to put in the work, but you could stick a hard airtank in there with an OPRV. If you set the OPRV just right you can get of multiple clips with one fill.
You would also need a regulator on it if you wanted consistent range on each shot. A drawback of hard tanks is that once the tank falls below the pressure needed to fire darts, the rest of the air in the tank is worthless. This is why air bladders are better for small applications, because they constrict as air flows out of them, and hence, maintain the same pressure until they are almost out of air. If you wanted to go with a setup like this
, though, an external hard tank would be great. These
are great hard tanks.