alot of people will just check the feedback score, so number of feedback received and feedback score, and won't bother going through all theitems you've bought. If I came across a seller who had done this I wouldn't suspect them as being dodgey, just the same as you, trying to get your feedback up so people will buy!
Type ebook into the search on ebay, it will come up with all sorts of rubbish that you can but really cheap, you pay 50p on paypal (or however much it costs) they'll email you the ebook or email you a link to the site if it's a website, and hey presto you get pos feedback! lol
Some people even sell pictures that they email to you, (either nice tropical islands or er... their girlfriends) which are also cheap... for obvious reasons!
Alternatively just but some cheap cds and dvds, they shouldnt cost much and in most cases you can re-sell them anyway.
Get a paypal account set up if you havent already as most buyers will want to pay via this, also sellers prefer to accept paypal too. this will take about a week but again it's worth it.
Good Luck