Maybe it'd be easier to fly to London first?

In any case, I recommend you look into other options for flying around Europe as well. I'd think there's a lot of stuff about this on the budget travel forum - references to sites like dohop.com and skyscanner where you can compare LCCs' flights etc.

www.easyjet.com - easyjet, I think, fly to LJU from both London Stansted and Berlin

http://www.adria-airways.com/ - Adria Airways tend to have pretty good deals to LJU as well