I just found this exploit about an hour ago and put it to the test. Just so you know, traitors can always defuse bombs and so can the owners of them. If you set the C4 timer to 10 minutes then you have a mere 20% chance to defuse the bomb. I do it 10 times in this video then show my trying to defuse it normally, and then it explodes.
I'm not going to say how you do this, but just know that you can do it.