This seller is shocking, forcing people to leave feedback isn't going to give him (or her) the best comments and as you've said it is against eBay's policy. Also it could put off potential buyers because they will be able to see the feedback that he has left for other buyers.
I have a policy of not leaving feedback until I have received feedback. I clearly state this on a note that I put in with my items and ask members to contact me prior to leaving feedback if they have any problems. I'm no expert but I've not had any problems yet. If they've not left feedback after a week I send them a polite message just asking if they've received the item. I think this is quite subtle and polite and so far it has resulted in positive feedback being left straight away, which I of course reciprocate.