As I understand it, no.
Once enrolled, the system's software does not allow any way to unenroll.
Indeed, if you have opted for an automatic draw on your bank account, it will continue to draw on your account ad infinitum. Or, at least, until somebody in Washington figures out how to make it stop.
And, of course, you've got to know the guy in Washington who figures this out...
It's easier to quit the mob.