Cork is closed cell so any product won't soak in. There are Cork Sealing products that can be applied as a single coat. http://u-40.com/corkseal.html
It enhances the color of exotic corks, and does make it easier to clean. It is definitely not a high gloss product.
Another option is to use Tru-oil or other gun stock oil - sold at Lee Valley as Danish Oil. It is applied with many thin coats, though it will darken the cork.
I used a product called Terra Nova Natural Oil from Windsor Lumber. It is the same stuff you use to condition cutting boards and wooden salad bowls. The grips look great and stay clean, but....on the river, if the grips get wet, they get very slick until they dry. I wouldn't do it again (I might even lightly sand the grips I have treated to get rid of the sealer). What ever you use, try it out on your back up rod first and see how you like it. It isn't for everyone.