app engine dynamically run code in a backend

Currently a user initiate an action, then a task is being queued and my code is being executed.

I want to allow the option to use a backend instead of a task.

What would be the best approach?

If I set one backend named "ExtraPower" to be dynamic with 1 instance, then... what? What should I do to activate it (with certain parameters)? Which URL should I call excatly?

Alternatively I read I can use the Pull queue, which is fine开发者_开发百科, but then again, how do I tell that backend to go and lease a task to process?

You can enqueue a regular (push queue) task against a backend. How to do that is described here.