It is the year 2000 and Joe has committed a crime in a small town in central Europe. When the police calls all adults living in the area to voluntarily provide a DNA sample, Joe knows he's in trouble. He wants to fool the DNA test, but he doesn't understand much of the process. He has one week to come up with and implement a solution.
Joe knows from popular TV shows that a sample of his cells would be taken by swiping the inside of his cheek with a cotton swap. The cells would then be processed into a fancy diagram with small lines and if his diagram lines up with the one from the crime scene, he'll end up in prison (that's all Joe understands of the process).
Joe wants to coat the inside of his mouth with a substance that would produce different or additional lines on the diagram to "prove" that he is not the perpetrator. But he doesn't want to go all Hannibal Lecter and commit cannibalism to do so.
How would Joe try to fool this DNA test?
Answers should keep in mind:
Joe doesn't know enough about DNA profiling to be sure his idea would work. Asking another person (online or in person) is out of the question because it would lead to his suspicion.
It's the year 2000. The internet was a thing back then, but by far not as all-knowing as now. All solutions must have been available at that time (e.g. in a library or popular media, through anecdotal stories or widely spread missconceptions).
The solution doesn't have to actually work, but it must be plausible enough that a person with limited understanding of the process would assume it works. It must not be obvious (like having a visible amount of fresh blood in your mouth).
The solution must not require the commitment of a serious crime (like cannibalism even if that's technically not a crime). Burglary or deception is OK.
Answers will be rated by:
Ease of access to information (popular rumors will be rated higher than scientific papers)
Ease of access to materials (no exotic chemicals or materials a normal person wouldn't have access to)
Plausability. Whether or not the solution actually works is completely irrelevant for the rating, but it must sound believable.