Think Ryanair PIK route would work even though BMI/BA fly in to GLA. Works from Stansted even though Easyjet and Flyglobespan do GLA, and competion from other London airports. Think it would actually do quite well as would be only loco route to West Scotland and would do a lot better than Jet2's EDI.
Very unlikely Ryanair would do it though as they generally dont like MAN's charges - although DUB does pretty well from MAN.