hotlink protection without a referrer

[kieranmullen]

Testing a website I was working on I forgot that I changed my referer in firefox to be blank because I wanted to search all of craigslists at once and CL was blocking the search engine which consolidated them all.

So rather than change it in firefoix I went back to test in ie (bleh)

Are there other hotlink solutions that work that dont depend on listing all the sites you want to block from and dont depend on a reffer being sent?
Thank you

KieranMullen