Alan:
The responses from used bike shops and such continue to trickle in (I got another one this morning) and I'm about 90% confident I'll find a reasonable bike. Enough to go for it. Nothing confirmed, and the rental scene looks particularly scarce for touring (it's pretty much all intra-city stuff in Berlin it appears). I'm pretty confident I'll find a bike for >350 Euros that I'll try to quickly sell, or I'll spend a bit more and try to get a decent price upon my leave.
Admittedly this is all a hassle, but for some reason it appeals in ways the whole boxing, etc. shindig doesn't. YMMV.
Lastly, when I started checking around weeks ago it seemed the West and South of Germany had much more along these lines. From what I recall you shouldn't have trouble renting a bike in Munich....recumbents, however, I wasn't checking for. Good luck to you, and if you're connection is via Schiopol I'll wave to you in the line at passport control (figuratively speaking). I'll be the bike guy without a bike.
scot