I have thought about that with a custom pin that I am ever so slowly designing - with considered a thin metal disc with a post that passes through to lock in that sits flush the playfield top but you could go for this sort of thing as well with plastic.
I also am considering a disc recess in the playfield for a special insert that houses a proxy sensor to replace the in-lane switch / and associated slot to get the proxy very close to the ball but on top giving a very smooth and flush finish - reducing maintenance to practically zero once set.
