Raggie, you have an interesting idea, and I decided to do it just now.
I pulled the incandescent bulb out of my Minimag just enough to be able to touch the leads of my DMM to them and check the polarity. After I had established which side is positive and negative, I took out the bulb and held in a 5mm. I had to hold it a certain way to get it to light up. When it did light up, it wasn't very bright at all. The incandescent bulb was many times brighter. Even though it is a 5mm LED, it wasn't as bright as a 5mm driven even at specs. It was dimmer than the an Arc AAA or CMG Ultra-G.
So it works, but isn't very bright at all.