it'd be a waste. The radar detectors pick up mostly by line-of-sight. You'd be really hampering their abilities.
I think there are a FEW radar detectors that actually utilize a separate detector module that you can stick up on the windshield somewhere inconspicuously and don't look like detectors at all. look for em.
Also, usually in radar detector unfriendly states/areas, you'll have the cops running radar detector detectors... which will mean that unless you get a good detector that can block or stealth mode itself out of the detection from the police detector detectors, you'll be screwed no matter what.