An easy solution would be for Norway to retain control over the islands but they are far-off and greatly coveted by Scotland as in OTL.
One can do it later than the Viking Era. Look at all the marriages between Scotland and Norway that came close to a personal union.@The Professor An interesting proposition! Though that would require a more complete subjugation of Alba by the Norse in the height of the Viking Era. At the same time, such a policy of autonomy might backfire in terms of Norsification(?) as Gaelic was already prevalent and by their proximity to Scotland might become Gaelicized instead of the other way around.