Winging it here, but was I correct when I said that the step sequencer produces a MIDI clip right in the track view? That's what I remember happening when I played with the step sequencer and Addictive Drums.
If so, you could select the track in your timeline that contains this MIDI data, drag in the time ruler (top of the track view) to select only the new pattern you have created with the step sequencer, then click File|Save As... Then -- in the Save dialog -- next to "Save as type," select MIDI, give the file a name and tell it where to save. I know there are four MIDI types to deal with, and I can't help with that, but trial and error shouldn't take too long.