Just Learned this trick today. Bonus feature!Funny - that occurred to me last week while testing TZF2's. The one I was testing had a problem - the fixed delay wasn't coming through, so instead the unit was behaving like a vibrato pedal. And the vibrato was really sweet sounding, and with speed ramping it's even cooler.
There's a hack for getting vibrato - Balance the pos/neg switch right in the middle (just like getting the in-between settings on an old Strat). It's really easy. This gives you the modulated delay with no fixed delay mixed in.
I just got some samples of 3-position switches that make it vibrato in the center. If they work out, future TZF2's might include vibrato without having to balance the 2-position switch in the middle.