Tier 2 MOR - Switch sponsors?

I work with the same religious organisation as an individual who has a Tier 2 MOR visa. At the time our UK charity was not registered as a sponsor so they obtained sponsorship through another religious charity who provided their oversight & management but also enabled them to establish a religious project collaboratively. Now that our UK charity can issue a CoS, we'd like to sponsor them upon expiry of their current 3 year Tier 2 MOR (May 2016).

1) I've read up on the supernumerary role; that seems like a can of worms. But it's not a vacant role as they are already doing the work. So it's over an above our normal staffing requirements now. As they created the project, and it's unique to them (e.g. pastoral support), we wouldn't replace them and the work would stop.
2) Although their existing sponsor would do so again, we'd like to sponsor them under our license as the other charity has done much already and graciously helped them set up their ministry. It seems like the logical next step for everyone - but is this like starting all over for the individual? A RLMT would seem necessary if #1 isn't possible.
3) What does this fall under - extension? They would not be changing roles only sponsors - so is it just a change of sponsor and back to #2; starting all over?

I feel like I have circular reasoning and questions!

Thank you in advance for any input you provide. Mike