Hey Barongreenback,
There are some good suggestions in the previous answers. keeping the kite low (over the water) will be better for the ribs but a harder walk up the beach,

a seat will stop the rib pain but could injure the precious family jewels as the leg loops strain at your groin

or landing and walking carrying the kite are all good ideas. It could just be that the spreader bar is too narrow for you which adds to the rib compression you are experiencing.
As you get more proficient, you will want to ride with a waist harny anyway, so maybe better to stick with what you have and find a better way.
A lesson in riding upwind from a good instructor who uses either a boat/jetski and or radios is an even better way to reduce the amount of walking involved as they can point out problems that you are possibly unaware of, which are inhibiting your upwind riding ability.

If you are already up on the board and staying on your feet, but are just going downwind, it is usually a simple matter of changing a few small things to acheive your desired results.
See ya at the beach,

Darren Marshall
Australian Kiteboarding School