Freeswitch support G729 Passthru, means proxy mode.

at fs_cli , type “show codecs”.
“codec,G.729,mod_g729” must be there.

By default conf, G729 is not allowed on any SIP profiles, so you have to modify vars.xml.
You will find the following lines:

Replace them by:

Then in FS console, do:
sofia profile external restart reloadxml
sofia profile internal restart reloadxml