We've flown Air Asia X and assorted other hinkey little LCC airlines around here with my 170cm board in a bag. We've declared it as "sports gear" and just sucked it up and paid... the extra US$100.
We've had good luck. No questions at all with Air Asia X but we misunderstood what the Firefly webpage was talking about regarding sports gear... we had 20kg x2 check in and 32kg of kite gear. Firefly webpage said 16kg sports gear each so I had prepared to split the gear into 2 bags, so it'd be 20kg x2 plus 16kg x2... what the ACTUALLY meant was, you were allowed 16kg as part of your 20kg check in
However, they let us on the plane without extra fees or hassles at all
just an "Oh, I see - let me check with my supervisor..."
That's one thing I really loved about Malaysia and Thailand - almost everybody has a "How can we help?" attitude when it comes to dealing with problems. Here in Japan and back home in NZ, the attitude is more of a "How can we hinder you?" even when you know all the rules and exactly what has to be done...