How to switch shorts in a half ironman

Just assume that you won't be able to make a full change. You might consider going with two tri shorts instead -- even doubled up, they'll dry faster than bike shorts during the ride.

I have also worn a pair a compression shorts (Nike Pro) in several IM's.  Just wore the shorts under my wetsuit.  Slipped on normal cycling shorts in T1.  Removed cycling shorts and slipped on running shorts in T2.  Has worked great for me.  Practice a few long rides with whatever you decide to do to make sure it works out ok on race day.

Good luck.

I ware my Speedo Jammer swimsuit for the whole triathlon.  I am 170 lbs so I there is a fair amount of weight on the seat with out any padding but I seem to be just fine for a 3 to 3-1/2 hour ride and can run after a 3+ hour ride in the Jammer Swimsuit with out any problem.  I would hate to have to change shorts in the transition which is why I ware the swimsuit for the whole event, but If I couldn't get around it I would place a towel on the transition area and when I get there wrap it around my waste like a Lava Lava or Sarong then change the shorts from under the towel while standing up.  You will defiantly want to practice this to make sure you know how to tie the towel so it doesn't fall down and how to change the shorts with out flashing anyone.  When tied correctly (ask any Polynesian for tips is you need help)  you can tie it in 2 seconds and it will stay up all day long.  Others may have better suggestions on how to do this with out a changing tent, but that is what I would do.