[From another thread about a flat-key instrument session at Whitby]

[B/C melodeon player] theoretically you can play in any key, provided you can find the notes!
Yes, I was told that the recorder is a chromatic instrument.
Would help if I had chromatic fingers though (or is it the brain that's too slow?)

The problem with this situation is not playing the notes (you just need to stop telling yourself you can't) but playing them loudly enough - you'd be competing with melodeons, clarinets, saxophones and brass.

You might be audible using a sopranino recorder, which would probably have the right range and okay fingerings for about half of what's likely to be played. I'll probably have one with me and I'm happy to lend it, though I have a couple of much louder flat-key-friendly gizmos.