Basically what I need is an Irish diaspora concentrated at a specific point and in the circumstances where they can declare themselves independent and a successor to the Irish state without getting squished.
Basic idea (very basic I might add) is that a large enough amount of the Irishmen serving in the Spanish military during the Age of Discovery decide to settle themselves on a Carribean island, for the sake of arguement we shall say Cuba.
So they settle down, making a fairly respecable Gaelic speaking minority amongst the Spanish, a few of the Irish nobles being governors and such. The British take the island during some colonial skirmish with Spain and keep it, leading to even more Irish migration to the island.
So, something happens which leads to the dissolution of the Irish Parliament, a surviving *English Commonwealth or an *Act of Union. This pisses off the Carribbean Irishmen who declare themselves the successor to the Kingdom of Ireland, appoint themselves a king and basically tell Britain to fuck off.
This is probably streching the realms of plausibility somewhat, I'm just floating it due to Rule of Cool.