I have a sportbrella for shore use but you have me thinking it might be possible to rig it with some kind of adapter in a rod holder or scupper hole. Unfortunately the structure is mild steel if I remember correctly.
http://www.sport-brella.com In researching beach shelters I found that they are mostly pretty wimpy construction wise, including the sportbrella. Nothing like Stringy's awesome bimini which is something purpose built for watercraft use and designed to catch as little wind as possible.
I think it's a case of getting what you pay for, cost vs benefit etc.
If you find a great solution please share your results.
Chris