According to the Schweizerischer Hängegleiter Verband website, pilots who are not resident in Switzerland are allowed to fly here if they hold a IPPI Card of level 4 or 5. The relevant section of the FAI website states that level 5 is required to fly cross country. All pilots must have third party insurance cover of at least CHF 1,000,000. Documentation must be carried with you.
The SHV website also states that non-commercial occasional tandem flights are allowed, if you have a valid foreign tandem licence.
Foreign pilots may acquire a limited SHV membership to enable access to Swiss meteo and airspace information.
More definitive information can be accessed using the links above.