Last summer when I traveled to Maui the only board I took was my skim. I used a regular Cabrinha travel bag - the non-golf variety. I took my 3 kites out of the bags and wrapped them around so they protected my skim very well. I also used my harness and lycra top to cushion certain areas. My board arrived there and back perfectly. It would be pretty unlikely that you can carry your skim on - especially since most airlines now go out of there way to be rude, and unhelpful.
Although it always depends on the person.
If you want to avoid the $100 fee always go curbside check in with your bags. Approach the bag handler with a $20 in your hand, and ask him to check your bags. He might say something like, "Hmm, that bag might be over-sized" or "Not sure if I can put that on without a fee". That is just code to let you know that he has not seen your $20, or expects more cash to do the job. Believe me these guys could probably put an elephant on the plane for no additional fee if they wanted to.
I have never seen anyone from the airline question them, and I have done this 10 or 15 times. 99.9% of the time your bags will go right past the nasty people at the check in desk and straight on to your flight. Plus you are up $80, didn't deal with the nasty people at check in, and he is $20 happier! Its a win win the way I see it!
Also, this seems kind of obvious, but be nice and respectful to the guy that is helping you out. Greet him with, "Good morning, a thank you, etc." - believe me it goes a long way to determine whether you bag ends up in your destination or 2000 miles away from where you are!
Let us know about your trip, and upload some photos!