This question bothered me quite a bit while I was trying to decide between gear and hst. Experiment a bit and you will find a way to make it work, sort of. Find a clear place where it won't hurt to tear up the ground a bit. Set the tractor moving forward with the brake pedals disconnected. Turn on the cruise control. Step on one brake pedal, I believe the left one. The tractor stops. Repeat the procedure and step on the right brake -- the tractor turns with the right rear locked. I don't remember which one, but only one of the brake pedals shuts the cruise off. It isn't too hard to see how to disable it if you feel the need. Just be careful with the cruise control since you will need to shut it off with the switch from then on.
I thought I would be doing that as a first "mod" to my tractor, but found out the thing was maneuverable enough that I didn't really miss the turning brakes at all. I thought I would just have to have them since I used them a lot on my previous, smaller tractor, but I get along just fine using two wheel braking all the time.