The OpenCockpits CDU/FMC really misses an EXEC light.

I have made two options on my DIY CDU:
1) A 3mm bright green LED in one of the holes on the side
2) Two 3mm bright green LEDs mounted inside the EXEC button.

This second options works very well!

After half a year or so I finally made a front plate for the CDU-bay. At this point I do not have have the lower EICAS or the second CDU installed. So it is just a board that is painted grey.

The CDU is mounted is such a way so the board goes in under the CDU and the CDU then is locked via screws.

There is a small video about it.