Actually, it looks like Ryanair doesn't fly from Hahn to Dublin.

Connections through Stansted are much better than Charleroi - lots of flights CIA-STN and STN-DUB.

The cheapest ROM-LHR fare I can pull up works out to about EUR 175, so it looks like this idea is going to be much more expensive than the low fare airlines. But at least you'll get looked after better if you misconnect.