Bind it up gently and hope for the best. I use panty hose for tying up tomato plants an such and have had good luck with using them. I asked a few ladies at work to save them for me and Wow, I had a good supply in no time.

make sure you pad the base of the tree to keep the trunk from wobbling around and causing root damage. bunch up some newspaper and pack it into the top of the pot and tape it down. then move it in a car (get a zipcar or cab if you have to) and make sure you put it in a place that gets similar sun.

I found my lemon tree to be especially resilient (approx 3’ tall). I moved it in the dead of winter 5 blocks just by holding the base of the tree steady and walking slowly between the two apartments. I didn’t tie anything down or wrap the foliage in plastic. Even worse, I cut the roots back and transplanted it about a week later into a new pot.

Your tree should be fine if you stabilize the base, gently wrap the fruit and foliage in burlap to keep the fruit from moving too much. Once your tree arrives at its new home, give it a good watering and put it in the same amount of light it was receiving previously. The foliage may wilt and the branches might sag but it should come back within a day or two.

There are many forums on growing citrus available with more info on Gardenweb.

I just moved my citrus tree (about 3' tall with the pot) some 800 miles across the country, and didn't lose any of the baby citrus hanging from the branches. Make sure you stabilize the pot, and definitely keep it inside the car with the windows up. You can wrap the tree in cloth so that the branches are bent slightly upward, and tie it with twine or string (but not too tight!). I wouldn't really worry too much about hurting it, citrus are tough little plants.