You can have some items pushing for a predetermined time by playing on the subscription requests on an existing permanent session (which is also serving the continuously pushing items).
Your page can leave the items unsubscribed, then perform "addTable" upon a user action and perform "removeTable" after a timeout.
All you need is some protection mechanism on the server side, which prevents a user from getting continuous push from an item that is supposed to only supply temporary push, by subscribing to it from a fake client. This is not easy to do, but it is possible, leveraging on the Metadata and Data Adapters.
However, this would not prevent a user from setting up a client which subscribes to the item at regular intervals.
Do you think that this way is feasible?