in May, there's too much (!) snow at the Stryn summer resort, and they simply can't open the roads up to the mountain! it normally doesn't open before the first weeks of June.
Folgefonna (summerski) may be an option, not that good for freeriding, but the park is often better than Stryn's.
An other option is Juvass in the Jotunheimen, but they may open later too, same problem (if too much snow can be considered as a problem ;) as Stryn.
Consult the forum on http://www.friflyt.no
wich is a Norwegian ski/snow etc magazine!