Q:

How do you minimize the impact of a politically necessary "poisonous" team member?

I am currently part of a project team evaluating the products of a vendor to develop an integrated solution to several of our legacy systems.
I am not the project manager on this particular project, but the designated project manager and I have a very good professional relationship, and I know that she values my feedback on project management issues.
Our main problem is the volunteer we are working with.  
Our parent organization is a non-profit, membership-based organization with a small core of full-time and temporary staff.  However, it is common for these staff members to delegate decisions or even entire projects to volunteers from within the organization.
We have been told by the parent organization staff member (let's call him Bill) who brought this volunteer (we'll call him Mike) on board that he (Bill) "doesn't understand the technical details", so Mike was brought on to "tell him if our plan makes sense".
Unfortunately, the volunteer sees things very differently.  He has made it very clear that he feels he is the project manager, and attempts to take charge of every meeting, regardless of whether it is an internal meeting or one with our vendor.
We have repeatedly asked Bill to speak with Mike and clarify his role, as Bill consistently tells us that Mike's role is simply to act as a SME.  Each time Bill says he'll talk with Mike, but after every conversation where this has supposedly been "fixed", Mike demonstrates the exact same type of behavior.
While it might seem easier to simply let Mike lead, it has become very clear that doing so would be a disaster.  His background is from a relatively small IT environment (albeit in a leadership role), but his project management skills are non-existent.  He has yet to fulfill his role as SME, and has literally wasted months of project time by providing irrelevant documents, attempting to radically redefine the scope of the project, and generally causing problems. 
I have already told my management team that I do not believe the project can succeed until the problem with Mike is fixed.  Both my supervisor and the project manager agree with that statement and openly support it.  However, due to the politics it seems like we have to proceed anyway.
Are there any strategies that can minimize the damage that Mike will do, while acknowledging the political necessity of not insulting him?  I keep holding out hopes that he'll be pulled from the project, but it seems unlikely.

A:

Mike is doing exactly what Bill asked, as evidenced by, "tell him if our plan makes sense," and reinforced by several role confirming, fixing conversations that have changed nothing in Mike's behavior.  In fact, with the order of "tell me if their plan makes sense" as his mission, Bill has given Mike some accountability of project success and, with it, authority.  Therefore, you can expect no change from Mike's behavior.
This is a common symptom of role ambiguity; or role sharing; or unclear, blurry scope lines between roles.  There is only one fix:  remove one of the roles.
So I guess the PM's alternatives are 1) to do nothing and continue plugging along with the project's success and her reputation at severe risk or 2) to escalate in a very formal way--face-to-face meeting with all required principles, documented--with the outcome of role clarity, e.g., he or she goes away, as a desired result.  
Alternative #1 is not really an alternative with a good ending so I think escalation is your best bet.

