[tunabreath]

There is a little mod that I've heard of working, but it requires some work:

Basically, remove the plastic nozzle below the chamber (the one that holds open the retainer on the mag so that the BBs can feed into the gun) and drill a small hole in it. Cut a tiny segment off of a very thin o-ring and glue it in the hole, so that a tiny nub sticks out inside the nozzle, enough the catch loose BBs, but not enough to snag fed ones.

Never tried it myself.