Well you could add a querystring to your url:
and use JS/jQuery to extract this value and modify the content of the page or, more usefully, just change the class of an error-message paragraph from, say "error-no" to "error-yes" so that it displays on the page.
This is not a fully-robust solution as it is trivial to edit the address bar - but, of course, you won't be relying on this 'fail' value!!
Preferably you should add PHP to your main page which displays different content according to whether they're log-in (or email verification) was successful. It is possible to dynamically insert a JS/jQuery script to run when the page loads, but if you are doing this you might as well just use PHP to modify the page.
Personally, I use the same page to display and verify the form, only re-directing on a successful log-in, but I get the impression you don't want to re-write too much.