Find a gym near the places you'll be staying with a daily or weekly rate. Go hop on an exercise bike for at least an hour, a few times each week. I bet that'll keep you up to speed well enough that you won't notice much difference. Personally, I've never bothered riding enough leading up to a tour to be considered "training" anyway. My legs will get pretty beat the first 3-5 days, but after that it's all good. I actually went on one tour in February after probably not riding at all for a couple months(WI winter and moving to a new apartment). I was a little worried that time, but after the first three days, no big deal. Try to get on an exercise bike if you can, but if you can't, I say don't stress too much about it.