Honestly, you probably won't even need one. The places that put the fake soda can over it are going to gouge you for an extra insurance policy that you don't need.
The rolling retest takes about 7 seconds to do, and you can easily do it while in another car's blind spot or ahead or behind somebody. Most people don't even know what to look for.
For the initial startup, you can duck your head down like you're getting something out of the glovebox.