I know you're asking how to do this, but...I don't recommend doing this at all.
I'm still cursing the previous owner who screwed up the expensive cowl doing this. It's hard to stand on the outboard now, and the stock covers don't fit. It's a PITA to attach/disconnect, especially when the boat is moving. When I remove it it's going to look like A$$ cause the Yammy paint is a horrible match.
Are you talking about the all around stern light or just the aft facing one?
Unless you have another white facing forward, having the aft facing one only is not legal.
Not sure there is enough depth to fit the socket/mount for the pole either.