Google App Engine Pull Queue

Question

I am evaluating an application based on Java on Google App Engine.

I want to create a certain task within a pull queue which will be picked up by a worker (most likely managed vm) who will work basically indefinitely on that task. To make sure that the task is executed i want to make that worker lease a task from the pull queue for lets say 1min.

After that time i want to extend the lease if the worker is still alive (This makes sure it is actively doing something).

My question is now: Is there a possibility to block the worker from extending the lease in order to stop the worker?

If this is not possible i would have to make a call to the worker and make him delete the task, but if it was possible to block him from extending the lease it would be much more elegant, beside the fact, that i have to delete the task afterwards anyway