The Fulton model that Donna has found should work fine if you can figure out a way to attach it securely. Take advantage of the additional length. The longer a tongue is the less weight
will be on the hitch ball and the more stable the trailer will tow. Also this allows the trailer to be safely towed by a lighter tow vehicle. So don't chop off the existing tongue to install one of these. As an aside, all of the boat trailers for sale
at Bass Pro Shops have fold up tongues. If you can visit a Bass Pro you can examine them first hand.
I came up with an idea for an extendable / retractable trailer tongue that would be operated by a hand crank. I was going to patent it but when I did the research I discovered that someone in Texas had beat me to it. As far as I know no one is manufacturing one.