OK, If I were in your position................I would go to the store and buy a tube of "Quicksteel" epoxy/putty. If you have never used it, its awesome stuff! I would'nt quite say that it hardens up as strong as steel like they advertize, but I will say that its the perfect thing to build a handle out of. You just moosh it up and then form it like modeling clay into whatever shape you need it to be and in 20 minutes its hard as a petrified walnut. Its grey in apearance, but that never bothered me.
Some other uses for this stuff are:
Making a backing block for knocking out pins from a trigger group, or other assembly where you need a lot of surface area supported while pins are being hammered out.
Making a quick rear or front sight in a pinch. (My shotgun is sporting a quicksteel rear sight right now. 300 full house loads and its still going strong.)
Building up the grips on your target pistol for that perfect fit, or adding a thumb rest to the left grip panel etc. etc.
Replacing knobs and buttons on the stove, sterio, motor vehicle controls, lawn mower, you name it!
Plugging holes in your boat.
Building an arrow rest "horn" on your bowfishing rig.
I could go on all night but you get the point. If I were in your shoes, I would get that stuff and put a gob on your bolt handle and just "sculpt" it into a scull or whatever you want. A few light strokes with sandpaper makes paint stick to this stuff quite well so you can color it how you want.