Well, then don't take the oath.
I wonder if anyone has done that?
"Mr. Ghuns, do you swear that the testimony you are about to give is the truth, the whole truth and nothing but truth?"
"No. Go **** a duck."
A few have tried it over the years. They were all cited for Contempt of Congress. The one that comes to mind first is G. Gordon Liddy. He was jailed for it.