MS 150- training idea?

My husband mentioned today that he would like to do the MS 150 bike ride with his family this year. They've done it for about 10 years, but we haven't joined them because of time and distance, but can this year. I'm down, it sounds like fun, but the problem is that I'm not sure if I can last on a bike for an hour, let alone 5 or 6 over the course of a day (his family is hardcore about cycling).

I currently don't have a bike and probably couldn't ride it with the amount of snow anyway (I'll use a spare bike for the ride), but I do have access to the stationary bikes at the gym. Does anyone have a training idea so I can get ready for this? Is there something like a Couch to 5K for biking? It's not until June, so I have time to start!