Hi!
I believe that this is possible. For what are you using this MLPPP interface? Private environment (like connection to MPLS) or is uplink for internet? If the provider is giving you the line in a transparent manner, just assure you transport to connect to your own network through a public infrastructure, that should be no problem, as the line is transparent for provider. If this is connection to an external network (you can see this as Internet) depend on the provider if he agree to allow bundling for you.
Please issue some more details.
Cheers,
Calin