[Freeswitch-users] Trigger re-INVITE with different SDP during a call

Hi, Is there a way to trigger a SIP re-INVITE for a channel that has already been answered, and to make FreeSwitch offer a certain list of codecs to the endpoint? Let's assume the call is answered with PCMA/PCMU, then the user enters an IVR, now we know that he's going to join a conference. For the conference, I might want to enable G.722 and H.264 video (which should not generally be enabled for all incoming calls). I found stuff about codec-related channel variables, but no 'trigger' to tell FS to make a codec re-negotiation. Greetings, Roland