Attach two 2x4's to the underside of the crossbars, extending 18" in front of the beam. Attach seat to the top of the two planks, and let 'er rip. Or get different crew, that will 1. Go over the side, or 2. Get in the water and go.
Have fun, and DEFINITELY post pictures!
sail fast

Andrew Tatton Nacra 20 "Wiggle Stick" #266 Nacra 18 Square #12