Soulcatcher:Sounds like a coding nightmare though.
My first guess would be its easy to do.
They already send the partner's avatar, putter, ball, location, front and zoom views they could already send the grid parameters for all I know so it may be something as simple as:
ShowGrid(PlayerN)=True
If they don't send the grid, the server, knowing who the partners are, could just send it and show it.
If we wanted to also show where the partner's aim marker is, that would be much more difficult IMO as that is likely not sent to the server until the putt is struck.
I like the suggestion and would be very useful as a training aid. I could use some (= lots of) putting lessons!