[SR-Users] RFC-5766 / RFC-6062 compliant TURN clients?

I know this might not be totally on-topic for the list, but I figured the list participants might have experience in this domain, so I'm lobbing it out there... I've got some situations where I'd like to connect users who are oftentimes sitting on very locked-down networks (ie, corporate networks) to some SIP-based VoIP infrastructure, but the idea of opening random UDP ports on the networks in question is a no-go. As a result, I'm experimenting with TURN over TCP or TLS as a solution to enable connectivity... however, I can't find any clients that implement the latest specs (X-Lite 4 appears to speak an older version of the TURN protocol; QJsip doesn't work for me; etc. etc.). Do folks here have any suggestions for TURN-compatible clients? I care mostly about PC for the time being (ie, just a proof of concept) but a PC/Mac/Linux solution would be great too. Thanks for any insights, --rafal