Placing Regen on the tank is fine if the tank has taken damage.
The WHM plants themselves on top of the tank as they Swiftcast Holy. Everything is stunned. The WHM is fine. The tank can easily take aggro.
The problem here isn't Regen during the pull, it's the WHM's positioning being bad. The WHM needs to understand that Overpower is a cone and work with you. They also need to run with you.
Edit: Thinking about it... I'm not sure if that's what you meant? It's still worth putting out there, at any rate!
