There's another way to do it. The rear of your head unit should have a set screw where you can screw it down to something. You would have to take apart the sides of the console and get a strip of metal and loop it and screw it down to the head unit. It's much harder to do.

BTW, what head unit did you get? I've seen Kenwood, JVC, Pioneer and Alpine all have sleeves that have the mounting tabs.

Also the other alternative is get a dremmel tool and make your own tabs on that sleeve.