Play internal Roland drum module sounds as midi in GB?

It's easy enough to use my TD-9 Roland module as a midi controller for Garageband sounds. But what if I wanna record the native TD-9 sounds into a track in Garageband? I can't get this to work. I realize I could record the TD-9 as a real instrument track (using the headphone output from the module) but I'd like to record the midi information. Has anyone done this?