Just spray it on, then pull it off when you have a crash before contacting your insurers innit...
In all seriousness, if you're spraying the entire car - I'd notify your insurance, no doubt they wouldn't look favourably on you if you had an accident in a bright green rubbery clio instead of the silver(?) one you told them you had.
Just thinking, plasti-dipping a car would be ideal for a getaway car surely? Get some dodgy/obscured plates, rob a bank, drive off, peel off plastidip, fit proper plates, drive like a gran. You now are £84,742 richer. Or something.