Sounds like you've got the plan down pretty good. Don't bother with the aspirin. Try and drink as much gatorade or sports drink as you can instead of water. The rule is about 48 ounces of fluids over a 3 hour period. Do too much and you'll end up with a negative dillute.
I would still take some clean urine with you just incase you get the chance.
A high fiber diet with metamucil for the next couple days will help and then change to the red meat high fat diet.
Good luck