PTN won't listen to my reason, but I'd humbly suggest Washburn Island in Waquoit Bay for your couch skiiing shenanigans. Campsites, easy boat access, watersports in the the bay or boating out past the breakwater, sandy beach, no hassles. Really nice area. You have to reserve campsites in advance.
"Watersports" are really more Dakota's thing. That bastard loves nothing better than pissing on a chicken.