I can't just sit on a trainer and ride so I use a few different trainer routines to get my SST rides in...
Ramping through the gears, start in 50x23 and drop down a cog every minute so I get a good mix of spinning and rolling a big gear. Riding the Pyrenees some of those climbs will take 2-3 hours to ride and they get steep in places so you will need to have the ability to spin (saving the legs for the harder sections) and the ability to roll at lower cadences.
On offs, riding hard for a minute, easy for a minute and so on. Interval training allows you carry out more work over a shorter period than trying to ride at a constant pace.
Long intervals, the good old (it is old now
) 2 x 20min efforts or variations. Again can be done at normal cadence or lower or higher depending what you want to develop or to break up an effort.
Spinerval DVDs. We had these in a bike shop I worked out and they are actually reasonably tolerable and the workouts offer a good variety and encouragement. CTS or Friel one's were not as enjoyable. Depending on where you are you may find a bike store that hires them out.
If you are doing indoor workouts I suggest you use a hack bike, not a carbon frame and have a good fan and keep well hydrated. I would also use the winter to do some form of Yoga or Pilates to keep the body well balanced.