You cannot seriously back up such a bluff. You are not on the best of terms with the King of Norway. If he was to find out you were using his name for your own benefits, he could strip you of your lands and title.
Accept that the lands in the north should be part of the kingdom of Scots. You do not want any more blood spilled fighting for it. You could then put all your efforts into Orkney.
Strike him before he strikes you! You are from a line of powerful leaders and fierce warriors. You will not be driven from your own lands. Join forces with your neighbour, Macbeth, Mormaer of Moray and destroy your mutual enemy.
Which card will you play?