I have had good luck with putting just my board in a 157 length bag with nothing else in that bag. They look at it a bit funny and then I hand it to them and it weighs 6-7 lbs and I tell em its a waterski or or snow board and I haven't been charged..mostly AA or united. Then we pull out my 2 other 50 -60lbs huge wheeled duffle bags full of kites, gear, diving stuff, whatever and even though these bags are really heavy they look "normal" and they are within regs for weight limiatations so it seems to work. Also having a heavy board bag loaded with kites makes it much more likely to get your board damaged as th eboard takes the force of all that other stuff when they throw it around.
-Peter