When doing any dilution techniques, if you dont do any creatine-loading at least 3 days prior to the scheduled U/A, you'll end up screwing yourself. Drug testing has come a long way from the days when only drug metabolites were being checked. Creatinine and Specific Gravity are also checked and if they are not in the acceptable ranges, the urine sample will be ruled "too-dilute".

Read up on N2's Dilution "sticky" thread for tips on diluting (disregarding the 'aspirin' step).