Most people on ebay are net savvy enough so that if you put a contact email address in the listing, like
sales@mydomain.com, they realise that there is a website associatted to it.
Also you are allowed to link to an external page in your 'about me' page, take a look at
Ebay Articles there are a few ones on there that may interest you.
Also when you are posting items out you can drop a link to your site into the email you send to confirm postage, this is a great way as the customer sees you care enough to let them know what is going on and also then 'invites' them to take a look at your site..
The list is endless..