Getting the coup you just have to find some people who hate the British and love money. If the coup goes halfway through with members of the government, public servants , reporters and clergy getting arrested and some killed throw in a few riots with civilian deaths and have the coup plotters get taken alive and someone talks to save his skin.
Germany will be dealing with a few million pissed off Irishmen.
You do get how utterly shattered the "IRA" of the time was by this stage (and compromised), what you are suggesting is not nearly as easy as you seem to think in the first place.