Tap-tempo Loopers?/Band use?

[kmurphy@wyan.org]

hello, i am new to this board and can't search for some reason so sorry
if this question has been asked. 

I am new to looping but really turned on by it. I am trying out the
Boss RC-20 for a GC 30 day-er, I know that if I stick with the Boss I'm
going to get the XL-20 for the undo/redo features and inc./dec.
features but figured i'll practice with this while i've got it. 

For the most part I really dig the box however while practicing with it
to some recorded rehearsal tracks with our drummer and bass player i
found that i can not adjust the tempo until i save the track?? has
anyone found any work arounds for this? Creative wiring of a
footpedal/modification? It seems to me that a lot of the looping
information focuses more on solo uses, i am really trying to get a
handle on using it with a live drummer/rock situation. Seems essential
that you be able to vary the tempo on the fly. your experiences are
much appreciated. 

Kevin