Sequencer Mode Question

[A.S.P.]

Ok... here's something I've been trying to work out in my head, and on
paper, but I'm stuck on it...

I want to create a touch keyboard, where each pad has a trigger output.  I
want to be able to trigger an analog sequencer with a keypress, similar to
triggering a sample loop on a sampler.  I want to be able to use different
modes: 1) I press a pad and the sequencer plays its sequence once and
stops. 2) I press a pad, and the sequencer loops as long as the pad is
being touched.  

It seems to me that there must be a way to create a latch for a sequencer
that allows it to run through once, then when it hits the last step, the
last step's trigger will flip the latch and stop the sequencer again.  

With the second mode I would probably just trigger an analog switch that
would let through a clock pulse when the pad is touched.

Do any of you have any thoughts on this?  Suggestions?

Romeo