Setting up data on the server side for PageRequestManager events

To me the on-line documentation in this area is either missing, incomplete, or fuzzy. Here's what I'd like to do:

On the server side:

• register a data object (such as a structured object consisting of 2-10 strings) as a dataItem that not associated to a control but can be accessed by one of my client side PageRequestManager event handlers (like endRequest or PageLoading)
• populate the registered DataItem with data and then call the UpdatePanel's Update method.

From the documentation it looks that this is do-able but I don't see how it's accomplished on the server side.

Could someone provide me with a simple example, or at least a clearer direction on how to get this done?