If you're truly desperate, make an alt. BIG BLINKING CAVEAT OF DOOM: I do not recommend this. It arguably goes contrary to your terms of service, because it can look like alt abuse. But if you were an unscrupulous pirate, or if you were very impatient, or if you really really really wanted your Seal on the Jade Ocean and you can't get the 4 other pirates currently logged on to notice your tournament...
...then, really, who could blame you for creating a 2-pirate-minimum tournament, and entering it twice?
Although you can create 3 pirates on a single account, you cannot be logged on as two pirates from the same account at the same time. But you can create a second login, open the puzzle pirates client twice, and log in as a pirate from each of your two logins. Have one pirate create the tournament, have both pirates enter the tournament, and then just wait for the whistle. In this case, you'd want to set the tournament for the shortest wait until start time possible (5 minutes), just to get the dang thing over with.
If you're going to go this route--and do note again that I do not recommend it--make the tournament unrated. This is very important if you don't want your innocent Seal-hunting to get you banned from the game. Some very unscrupulous pirates have used alts in order to artificially alter their puzzle standings. That's alt abuse. Oceanmasters frown upon it. So uncheck the "Rated" box to ensure your little tournament doesn't look like that.
But hopefully you won't need to do that, right? ...Right.