Candlewax! Seen it done, works a treat and lasts for yonks...
Rub into the bolt and run the sail up the foil a couple of times, applying abit more if you think you need it. I have been told that it doesn't harm the dacron.
Personally -= I'd avoid anything waxy as it is prone to picking up rubbish, and evntually staing as well as binding. Id go for one of the 'dry' silicone sprays (I usually use either the Harken or Lewmar - no difference that I can see). It transforms the way things move, and is worth every penny.