If i'm right, then the original light (that was a BMW accesory) had a metal clips not unlike a metal tools clip, one of these -roughly-omega shaped ones.
Check the clip in the 3rd image of this post:
My two carbs CSLs have the same holes on the dashboard. It probably was the place for a road map lamp. One has still the fixing clip on the dash. In the owners manual supplement for the CSL the map light is located in the glove box compartment but I didn't find any traces of it. Any pics or...
e9coupe.com
One like that would work, and even look period correct, albeit a wrong combo for Enoz's specific light.
No without further hijack of this thread: go buy this light; it's really helpful if you drive at night time with a co driver.