Can you set a specific elapsed time?

I have a rather odd question.  We have exercises that the user must complete in a specific time.  All well and good.  Now I've been asked to add a button whereby the user can opt out of the exercise partway through. The problem is that the user who drops out will register a shorter elapsed time than somebody who completes the exercise.

The whole course is based on the time taken, so I can't simply say the user failed the course, based on the click boxes not used.  Also, there is some branching, so it's difficult to set completion on the basis of slides completed.

I've wondered about setting a variable that says the user didn't complete the course.  (It has to be read by a SCORM-compliant LMS.)  It's been suggested that I could set a variable that artifically inflates the elapsed time to, say, 30 minutes instead of 5-7 if the user doesn't complete it.

Does anyone have any suggestions?  I've browsed Lieve's blog, but nothing jumped out at me.

Thanks for any suggestions....

Marion