I am not really sure how you would prove that. I had read on one case that a judge visited the website and viewed the Click Wrap agreement and choose to enforce it. Here is a site that covers all of this much more:
http://grove.ufl.edu/~techlaw/vol4/issue3/friedman.html
My guess is that as it is a part of the shopping cart system on my site now, they would consider it having exissted. Even before the click to accept I had a statement above the Submit buttons stating that by Clicking on the Submit button that they were agreeing to accept our Terms & Conditions, which were linked to the terms. My last software had the click wrap lisence built into it.