Another idea was to take Uristat or AZO (which he uses occasionally for bladder issues) so his urine is bright orange and they would need to retest after he has cleared the dye from his urine (approximately 8 hours to get rid of the dye).
These products do nothing to rid the body of THC. Besides, if a collector notices the bright orange color (which is an unusual color that is not supposed to be present in normal human urine), the sample can be determined to be "suspicious" and trigger an immediate sample recollect under direct observation. The collector would then process both samples and indicate in the "Remarks" space that a direct observed collection had taken place and the reason(s) why.

Youd be better off sticking with subbing with the QF.