Ouch... I think you're screwed, Man.

Oral swab tests don't swab cells from your cheek. They have you pucker your mouth, collect some saliva in it, then a spongy thing absorbs it. They will check your mouth first to ensure it is empty, and not allow any beverages or anything until after the test. And it has a control panel so if what they test is not saliva, they'll know it.

Your slim chance:

If your employee contract specifies that you can be urine, blood or hair tested, (if it just says "drug test," you have no loophole) and does not specify oral swabbing, you may legally be able to refuse - Claiming you're unfamiliar with this method and don't want to end up with a false positive on this relatively new kind of test. They might just say, "Take it or you're fired," but it might buy you a couple of days to get clean while they discuss your objection with their legal department.

These tests are mostly good only for detecting substances which are currently active in your system. Additionally, they detect THC directly, not the metabolites like urine tests often do. THC does not last as long in your system as some metabolites do. If you stopped smoking 1-3 days prior to the test, there is small a chance that your levels of THC will not be detectable tomorrow... But unlikely if you've been a habitual smoker for as long as you have.

I'm sorry... This sucks.