I don't see anything wrong with Wideroe as a callsign. It's the ATC units who are in the wrong for using the aircraft registration when you've filed a flight plan using an accepted ICAO company R/T designator.
If they can't handle it on the ground then, unlike 121,9_za's comment the registration should not be used. It should be the 3 letter FPL designator for the company followed by the flight number exactly as written on the Flight Plan that is accepted and correct.
So - if they can't say Wideroe - then it should be "Whiskey India Foxtrot..........(Flight Number)............."