Workaround:
Set up a prize for a manual prize for a fixed amount (you will know how much it is when tourney starts so you can fill that in.
Set the display to be "High Hand: " and then you can edit this prize with the actual high hand and award it to whoever currently is the highest.
So, lets say you have AAAKK as high hand and Joe is the guy who got this hand.
you edit the display name to be "High Hand: AAAKK" and you award it to Joe.
then on your prizes cell, it will display the current high hand and who it is awarded to.
Any other mechanism for doing this will still require about the same amount of input (you will have to choose a player and you will have to type out the high hand (well I guess you could have a drop down list, but, it would be a big drop down list, just as easy maybe to type it in). So it isn't a bad workaround.
You may be able to do this with TD figuring out the amount by having it use a leftover amount for that prize, but right now I can't figure out how you would do that.
Just a thought