I use the following script to escape from the frame of a referring site. I'm no JS expert, so this may not be the best method to do it, but my original comments in this snippet indicate that it will do what you want with a little work.
The trick here is to use the "location.replace" function. This overwrites the current URL in the "history" used by Back, Forward, and the browser history list, making the current page (the one with this script) disappear from the browser history:
if (parent.frames.length > 0) top.location.replace(document.location); // Escape from any referring site's frame, but enable one-click "Back". --></script>
I think if you modify it like this, it will do what you want:
location.replace('your_new_URL'); // Redirect to new URL, but enable one-click "Back". --></script>
You might want to post over in the scripting forum for more options.