Carriage bolts are OK, as long as you don't mind the 4 lumps on the decklid. If not, try this:
1. Go to a vinly sign shop, and have them cut out a sheet of vinyl circles that are slightly larger than the 4 decklid holes left when you remove the wing.
2. Get some touchup paint the same color as your car.
3. Paint the circles you are going to use while they are still stuck to the sheet you received them on.
4. Let paint dry.
5. When the paint's dry, carefully peel the 4 circles off and stick to the decklid.
I've had mine on for about 4 years already, and haven't had to reapply them as of yet. Peeps always wonder how I covered the holes (since the trunklid appears flat) and they have to come all the way up to the decklid to see what I did.
It's a far better approach IMO and far better cosmetically.