One of the impediments to using mediaproxy2 is that AG does not seem interested in maintaining or supporting long-term fundamental compatibility with Kamailio/SR, as an OpenSIPS partisan. Perhaps I am mistaken on that, but that is the impression that I get.
A good approach is likely to be possible soon in Kamailio 3.x/SR with the use of the kernel-bound RTP proxy that was built into SER,
I do not exactly know how well it works at this point, but seems to me like a better approach if my perception of political difficulties with mediaproxy2 is accurate:
http://www.kamailio.org/docs/modules/3.0.x/modules/iptrtpproxy.html