Back Strain/Spasm Advice?

Last Thursday evening, I threw out my back, ironically, while racking my daughter's bike on vacation. This is not new. I have a history of lumbar vertebrae twisting to the right, towards my 3/8" shorter leg (long since adjusted for through the magic of orthotics). This is my first trouble since getting orthotics several years ago, and it's definitely not as bad as any of the episodes I've experienced in the past.

My "A" race this Saturday will no longer be for an AG medal, but since my son will also compete that day, I'd like to show up and complete the already-paid-for race. Since the injury, I've already swum 500 yards, taken an easy bike ride of the Sprint distance, and gone for a two mile walk. If I feel good on Saturday morning, I hope to let all the swimmers go, swim easy, ride easy, and maybe walk the entire 5k. I can't get into physical therapy until next week, so that's the best that can be hoped for, barring a miracle.

Since I've been through this a number of times already, the knee-to-the-chest stretch and Ibuprofen are already in place. The hot tub at the pool feels good.

Does anyone have any advice or encouragement to help a sore back through 5k? I promise not to push, and to be in PT the next couple of weeks.

Thanks. : (