I've read that 100% concentrate cranberry juice has sufficient levels of acidity to maintain the required level so as not to arouse suspicion - is there any reason to not use this instead?
pH is not checked to determine dilution. pH is checked to determine adulteration . Only creatinine and specific gravity are tested to determine an overly-diluted urine sample.

The creatine ingredient in those snake oil products will do no good when the product is consumed on the day of the U/A. It takes 2-3 days for the body to convert creatine into creatinine. Therefore, any creatine-loading must be done at least 3 days before the U/A.

Gatorade/Powerade, used in place of water, does help in the Specific Gravity dept. All of this, plus other dilution tips, are found in the Dilution "sticky" thread.