heya buddy...I got a super tiny brake light from some auto store.
Trimmed it down so its even smaller and welded in a bracket and made it into a high stop light for the mini.
To put it into perspective of how small it is it fits UNDER the rear rain gutter above the rear window.
Maybe you could use something like that and make it miniscule and tuck it out of the way so it can only be really seen when its lit up.
Just a thought.