[haste]

I'm not really sure if I understand your question. Do you want the players castbar to be shown on the raid unit you are healing?

If so: You can't really spawn a player castbar on a raid frame, but you can move the player castbar to the raid frame on OnEnter/Onleave.

Something like:

OnEnter = function(self)
   -- Move the player castbar to the raid frame we are hovering.
   local castbar = YourPlayerFrame.Castbar
 
   castbar:ClearAllPoints()
   castbar:SetAllPoints(self.Health)
end
 
OnLeave = function(self)
   -- Move the player castbar back to player.
   local castbar = YourPlayerFrame.Castbar
 
   castbar:ClearAllPoints()
   castbar:SetAllPoints(YourPlayerFrame.Health)
end

Remember that you also need to :SetScript() these handlers.