As has been discussed elsewhere, you can get insurance from ADAC in Germany (and likely from their Swiss counterpart) to cover you for third party liability insurance while you are driving on your US plates. You will not be able to (or at least I do not know of a source) be able to get comprehensive insurance and so if your car is stolen or if you have an at fault crash you are **** out of luck.

If you ship your car into Bremerhaven (for example) and flew into Frankfurt, you could go to an ADAC office in Frankfurt or Bremen and get the insurance which would enable you to drive away from the port after clearing customs. Also, unless your car is a bit of a beater, do not do RORO... and do not under any circumstances pack stuff in your car if it goes RORO (unless you want to see the sailors wearing your kit on your next visit to Hamburg).