I decided to replace the broken plastic head on my ignition key with epoxy putty. I made a small ball of putty (the kind you get in a stick) then inserted the top of the key. Then I began to press it out into the shape I desired. You can get creative here. Once it was close to the size and shape I desired I then let it cure. After it had cured I used a file and a sanding block to smooth it up and give it it's final, finished shape. I drilled a sufficient hole into it so I could keep it on my key ring. I used it for a long time that way. The guy I sold the car to used that key for years. If any of my others break then this is what I'll do...because I'm cheap.