I have found the TSA folks to be very polite. On the rare occasion that I or any of my belongings have been searched by them, they have been courteous and professional. I think a simple request along the lines of,

"You know, that last guy's shoes really stunk; would you mind changing gloves"

would be more than sufficient. And if you happened upon an uncooperative TSA agent, I would politely ask that s/he call over a supervisor (but I would be surprised if it came to that).