[Freeswitch-users] Verto re-INVITE equivalent

Hi, We have mobile apps (iOS/Android) and a website that uses FreeSwitch for audio/video conferencing using mod_conference. We are currently using SIP and considering to move to Verto for signaling. In our app users are connecting without video (not sending video) that implies a=recvonly and later on they can add video dynamically using SIP re-INVITE. How can we implement this using Verto? I tried verto.attach but it doesn't really generate a new local SDP on fs.. Any idea? Thanks, Adam