I know it seems very unlikely, but what if Charles I had won the Civil War and succeeded in establishing a sort of royal absolutism? AFAIK most of the other countries in Europe were busy with the 30YW so weren't really interested what was going on in the British Isles, so help is going to most likely have to come from within Britain itself.
Maybe if the Scots decide NOT to hand him over, and he uses Scotland-Ireland as a sort of springboard.
Discuss.