Hi Gaurav,
Unfortunately, there is no easy way to do it. I described below some solutions hoping at least one of them could help you:
1- To be able so differenciate the native VLAN from customer one's and to do that for several customers, UPE need to implement EVC/EFP (7600 with ES LC). This way you could do BPDU relay between the two UPE's per customer and send to the NPE's via the PW the customer VLANs. Only MST is supported and STP must be disabled on the UPE's
2- Transport customer BPDU end-2-end so he will see the VPLS domain as a single switch. It's usually not a recommanded approach because instability in one site can impact the other ones. Also you can't manage your blocked links per site as all sites share the same STP domain. Last thing is VLANs must match on all sites.
3- Last option, I have in mind is to develop some EEM scripts which will break the loop. For example, a script on UPE2 shut its AC unless the PW between UPE1 and NPE1 is down.
The following Cisco book explains how to use EEM to provide redundancy between DC connected via VPLS:
Interconnecting Data Centers Using VPLS (Ensure Business Continuance on Virtualized Networks by Implementing Layer 2 Connectivity Across Layer 3)
Not sure if it's usable in your environment so.
HTH
Laurent.
