Hmmm, if you are game, you can cut an access hole in the inner sill. The first cut, as they say, is the hardest, but done properly it gives you access you simply don't have. Check the pics of how I did my past Duetto by going to:
http://au.pg.photos.yahoo.com/ph/beatle_bayly/my_photosYou need to know the inner construction of the sill before cutting large holes as there is some internal bracing. I may still have the measurements somewhere but I basically worked it out by drilling a series of small holes and probing with bent wire to determine the location of internal lumps and bumps.
Failing that, clean out the drains at the lower edge of the sills and then give it a powerful squirt with water. Keep flushing at different points to dislogde any crud. Leave it to drain then spray LOTS of WD spray in there. You will need to buy a gallon or so and use something like a garden sprayer. A pressure pack won't cut it and you'll neeed to apply it on the upper inner surfaces as well.
Try to do this in the heat of summer and try alternating parking the car at angles so as to drain any excess. Also, if you can gain access, sticking a warm air source into the sills will assist purging the moisture. Even just a blow gun on low flow will greatly assist the drying.
After a few days of this, and an extended time to dry completely, go ahead with the fishoil/lanoline (using your new garden sprayer).