Here's what you should do. Walk over to Bayside Marina, during Christmas around 8:30pm, non-holiday around 8pm. Look for any of the cruise drivers hanging around Bayside Marina (Blue Shirts & Pants). Ask if any of the boats have small parties. The pontoon can hold a total of 10 guests (including children and infants).
Let's face it, it's Disney. Most guests that have an entire boat and a small party would be more than willing to share with you. Aside maybe a very special occasion (Anniversary, Honeymoon).
Bottom Line - You got nothing to lose by asking.