I don't think its possible for an extranet. It may be possible for an intranet but I think it may pose some challenges to implement, probably won't perform very well, will introduce complexity and be difficult to be sure it is secure. For those reasons its not something I would recommend without more research.
To access files on remote servers would require Impersonation with Delegation.
Note that mojoPortal uses Forms authentication even when it authenticates against Active Directory. To use impersonation I think you would need to use Windows Authentication and that would only work on an intranet or local domain.
Hope it helps,