I once saw a video of Jim Clark, Jr. (IIRC) using a tube-type speedloader to load an auto shotgun. He took this tube, which was probably 18" long or so, stuck it in the loading port of the shotgun, pushed forward on something (it was VERY fast and I couldn't see what he was doing too well), and presto!, he had recharged his shotgun.
I have no idea what the device was called or where it came from, but maybe it's what you're looking for.
DAL