Natively the cancel button just amends an href='#' to the call. So you would need to make a custom cancel button if you wanted to control the redirect.
This is straight from the "Magic Button" app,
"<a class='Vibrant Success' onclick='DoSaveCancel()' href='#'>Cancel</a>"
So you would need to add your end URL to the href.
Another option is to pass the "Cancel" URL via the original button push.
Basically it would write to a URL field, then your cancel button would use that URL in the cancel href.
Say my [Cancel URL] is field 20, you can add
&_fid_20="&URLEncode(www.google.com)&"
Then your Cancel button would look like:
"<a class='Vibrant Success' onclick='DoSaveCancel()' href='&[Cancel URL]&'>Cancel</a>"
