Easiest and cheapest these days is DUB-GVA direct with Aer Lingus. Special fares going for €28 one way plus taxes if you fly on a Tuesday.
Otherwise, you could try easyJet Belfast-Luton-Geneva. Have flown Ryanair Dublin-Luton and connected with easyJet Luton-Geneva and have never had the slightest problem.
Goodbye SR-LX MD-11 / 6th of March 1991 to the 31st of October 2004