I too am a bit short of the 4fun. I have done exactly what other mention here. Add a bit of foam in front of the happy feet. This essentially moves the whole happy feet system towards your feet. It works flawless for me in both my Super Star and 4Fun.
The key with happy feet is two fold:
Be sure not to pump much more then 15 pumps into to air only bag. I actually recommend no more then 10(ish). Point being is that if much more then that, you loose the main goal of this highly comfortable solution for your feet.
Also, be sure that you vac seal the bean bag portion of it. Many people think you are supposed to leave a little air in the bean bag area, and that only makes it sloppy and less control for your feet. Once you vac seal it... it's simply molded to you feet shape and can be very firm for great foot support.
Not everyone is going to love them, but they are a huge seller for us. Most people buying them for other manufacturers boats. Once they are set up correctly from the get go they really are awesome. I honestly can't imagine paddling with out them now.
Hope this helps.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body. But rather...To skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming... WOW !!!! What a ride!!!!!!"