Good thread! I'm sure there's many of us thinking of different ways to advertise and someone's "weird" could become someone else's wonderful!
Well, you can't place a referral link on your Ebay listing. I don't see the harm of including a business card with your website address in the parcel, as a business card is more professional. The buyer will either be curious to look at your website, or not.
I would tread very cautiously with that piece of paper. It's more "in your face" and you can't know how the buyer will react. You're not anonymous, so if the buyer is offended by advertising that bears no relevance to the purchase, he/she might report you to Ebay and your status as a seller will be affected.
However, the piece of paper is still a good idea. You could make up leaflets, pass them around to family, friends, work colleagues, etc, post them through letter boxes.
Good luck with whatever you do!