The email that I send upon shipment has:

Good news <#BuyerFirstName>!

Your item<#s2> shipped on <#ShipDate f=d2> to:

<#BuyerAddress>

Please take time to leave feedback for me when the goods arrive. Because it's such an important part of the online auction business, I want to build the best possible feedback rating. I'd really appreciate it and will gladly do the same for you.

in the invoice header (top) section, and:

eBay # <#AuctionID> -- <#Title>
http://cgi2.ebay.com/aw-cgi/eBayISAPI.dll?LeaveFeedbackShow&item=<#AuctionID>&UserIDto=<#SellerUserID>

in the Auction Lot (middle) section. This then gives a clickable URL to leave feedback