If you enabled multicast on ALL customer-A sites, then you will need to enable all customer-A VRFs for multicast - VRFs are configured on the PE router for MPLS. The MPLS 'P' routers (the actual core of the MPLS network) will need multicast enabled as well, if 'P' routers are Cisco, just 'ip multicast-routing' is all you will need on the 'P' routers (unless you need more control).
Tutorial
Details
There are two command-prompts. In one command-prompt we have the Multicast Tool running in listen mode, and in the other in send mode.
We are executing two commands in the send command-prompt: one by entering the input in the command-prompt, and the other by sending the contents of a file to the application. Both the contents are received by listen application running in the background command-prompt.
Then in the listen mode prompt, we give the command bye to quit that version. You may also enter EOF character or other commands like quit, exit, close, terminate, shutdown, hasta la vista, vanakkam, danyavada and danyavaad.
This tool is available as part of 'The Joy of Unix in Windows Tool Bundle':