Folks, something must be done to balance this thing.
I'm going along the supposedly well-trodden route of 1066 Dublin start. King of Ireland is easy. A successful crusade yielded me the crown of Jerusalem (well earned, no objections). A lucky pneumonia for my well-placed-matrilinial-marriage-to-a-claimant-begotten heirless relative gave me the larger Duchy in Wales (and consequently the crown of Wales). Nothing exceptional, I think.
What I think is out of all proportions is that I was able to invite to my court an actual pretender to crown of Scotland (and a potential, once his mother is dead, pretender to the crown of England in one) and make him marry matrilineally to one of my daughters. The wonderful Mr. Prince Henry of Scotland. His heir will have a claim on the whole damn Celtic world!
The reason I was able to invite him to my court is that the only thing (apart from base reluctance) preventing that was was his opinion of his liege. That is, as you all know, negotiable. This particular poor beggar had an imbecile heir and enough ill-wishers for me to plot his demise. New liege, a drop in opinion, Prince Henry is up for grabs.
Did I mention his claim was inheritable?