Asterisk adn Xtunnels

Does anyone know how to configure Asterisk with STUN and Xtunnels?
I can’t enable the port forwarding on the NAT, so the only solution seems to be Xtunnels.
With X-Lite softphone I can configure the settings about STUN and Xtunnels and all works fine, but now i’d like to use Asterisk on the same way.

Thanks in advance.