Something doesnt seem quite right here. I can understand the above posts but the examiner will need to send the renewal paperwork to the CAA and therefore presumably he will need to have a CAA examiner's reference. While there may be CAA examiners in Switzerland presumably any old examiner will not do in the same way that if an FAA IRated examiner were to sign off the IMC renewal in the Sates the CAA would not accept his sign off.
I appreciate that was not exactly the answer to the question you asked. I would agree that if you can find an examiner in Switzerland that is authorised by the CAA to renew IMC ratings then I dont see as far as the CAA are concerned they care what letter is on the side of the aircraft or where the renewal takes place. I agree that if the examiner does not hold an IRating that is valid in Switzerland then the renewal would need to be conducted in VMC but that should not be an issue.