Here's a couple things you might try. Get an epoxy based paint that is used for firearms. Brownell's sells some, and I think you can get them at other places. I have used the stuff on various gun parts like sights, and hammer extensions and it works well. I think the sell it in gloss or matte finish.
The other thing would be truck bed liner spray. That would put a matte textured finish on the scope that might look pretty good.
The main thing is going to be surface prep. Getting a little profile on the surface so the paint bites. Also you are going to have to cover and tape off all of the glass and the adjustment knobs so no paint gets onto or into them. I think it should work, but you are going to cover up any graphics or printing that is currently on the scope.