Actually, you might want to look at MainStage 2. It's a really elegant live applciation; you can set up a "concert" for your show, and then set up individual patches for each song, switching between them via MIDI program changes (or a mouse, if you want. But you get the idea).
It sounds like you have the DP sequencer running, and then you play a single part live. Now, MainStage 2 doesn't have a sequencer, but it has a new "Playback" instrument, along with a "Loopback" instrument as well. So you could record individual MIDI tracks as audio, and put each on it's own channel strip. You could then trigger playback, stop, rewind, etc. for each track, with realtime effects, etc. I think you'll find it as flexible as working with sequences. Of course, if you don't need all that, you could just have it play a file with a stereo mix of your song, and then have another track for the live instrument.
I think you'll find that MainStage 2 lets you create the ideal interface for live playing. You'll love it, even if you keep using DP as your recording sequencer. Although I of course recommend Logic Pro 9 as a sequencer, but DP is great software too. Both Logic Pro 9 and MainStage 2 are part of Logic Studio.
Orren