We usually put them in our hand luggage and pack lots of other things in/around them, socks, hats, gloves etc. At least you can then be sure they haven't been bashed around and damaged in any way.
I would cunningly disguise them as bowling balls and try and convince check-in that you are professional sportsmen heading out to the world championships (err..which this year are being held in Bulgaria). This will impress them so much that, once they have asked for your autographs, they will allow you free additional baggage and upgrade you to err.. 'super-economy' ..for your flight to BLG.