Multicast VRF with one single different channel stream

Hi,

We having a multicast vrf with a single RP point (provided by the IPTV provider) where we want to import a single IPTV channel from a different source (other provider).
The issue is how can we tell the vrf that a single multicast address is on a different (other VLAN interface) source then the RP? So our setupboxes getting the single IPTV channel source from the multicast cloud/vrf

Kind regards,

Michiel