You can allow an optional item on each scale response that skips to a non-existent item, such as "end" or "quit". That would take you to the end of the experiment. You can also visually separate that item using hieght top and width parameters.

See also:

http://www.empirisoft.com/Support/showthread.php?t=211
http://www.empirisoft.com/Support/showthread.php?t=25