[Lizard]

Hmmm...I don't think you can do this. You can get close:
1) Create a milestone at the beginning of your project.
2) Create a finish->finish dependency from the milestone to the task.
3) Put a lead time of 10 days in that dependency.

This puts the end date in the right place, but will not give you a violation or anything if something else pushes that end date later.