Unless you are at a very large event, most transition areas are not private and you will be changing in the open. It might even be against the rules to go nude for a moment. If you absolutely must change, you can hold a towel around yourself, but being wet and doing that probably is asking for a lot of headaches. My suggestion would be to use cycling style pants without a pad. Whatever the case, you'll be making some kind of tradeoff because there is no ideal solution.