Add checkbox when adding node and/or comment to subscribe to updates

I've been tinkering with the module and with the notifications module, what I would like, and can't find how to do, is to add a checkbox in the node add form to "subscribe to updates" to this node in the node creation form.

Is this possible or does the module currently only provide the possiblity to add subscriptions in the seperate subscribe form displayed when viewing the node?