A trip to your local motorcycle dealer should get you some cable lubricant. You can get a thingy that goes over the cable so that the lubricant is squirted directly into the cable. There are most probably 'proper boat cable' lubricants, but you can bet that it is the same stuff at twice the price!
CRC Lubricant (Marine Formula). It's inexpensive (at least in the US) and can be bought in spray cans or in volume for transfer to a pump spray tank. We spray down our engines with it as well to prevent rust. It doesn't harm wires or hoses.
LamacqS
