Setting the update attribute value on server in AJAX Call

In p:AJAX, we need to mention the target Ids in Update attribute. In business process, these target ids are sometime decided only after the server side processing is done.
Is there a way I can associate the update attribute value to a managed bean instance variable and assign the target ids after my business processing is done?

I think RichFaces has this capablity. It will be great if we can achieve the same in Primefaces.

I am using Primefaces Version 2.2.1. IDE is RSA 8, Server is RSA 8 Server.

[optimus.prime]

RequestContext.getCurrentInstance().addPartialUpdateTarget("clientIdHere").

[optimus.prime]

Also standard JSF APIs can help like PartialViewContext.