I found a way to code it in, not perfect but it works for now.
I added an extra section to the get_share_links function in class.yith-wcwl-ui.php (at the end of the file), added an image to the plugin folder and made it work via the wishlist.css. Take a look at my wishlist: http://www.playmoparts.nl/wishlist/?user_id=1, it is in Dutch but you will get the picture. You still have to create an account to see the wishlist, woking on that also.
If you want to use my files makes sure you check for file locations, they are for my site, and keep in mide that the changes in the class.yith-wcwl-ui.php are not update proof!
The files: http://http://members.upc.nl/f.westerhof/Wishlist.zip