On a past vehicle I owned the mirror turn signals extended past the mirror frame just a tiny bit. This provided a way to confirm the turn signal was indeed on while checking for lane traffic. I considered it a great safety enhancement. I've wanted this on my Hybrid so I experimented and came up with the following.

I opened up the mirror frames and installed small LED's I purchased from Amazon. I tapped into the sequential turn signal wiring connector using some spare Mirrortap blades I had.

Look closely and you can see a small o-ring I placed to help reduce water intrusion. The LED's come with dual locking rings so I was able to get quite a bit of pressure to seal the o-ring to the frame. The second locking collar should keep the first in place. Overall it took about 1 1/2 hours per side; I work slowly and surely...with this result.
One item to note - There is little clearance between the mirror skullcap and the mirror assembly itself. A small barrel length LED is necessary to fit properly.