I'm still not sure how to do the DTLS handshake. I was under they impression that I might be able to use the ssl:handshake and then downgrade again, but I realize reading your comment it will be much more difficult...
I will do that. Checked the archives after your comment and it seems use_srtp support is planned. My current understanding is that for dtls-srtp only the handshake is necessary for key exchange.