rendering controls out of a session context

[PJ6]

I want to render control output server-side not from a particular session or
in a particular page, and return that to an AJAX-style call from a client to
dynamically re-render a portion of a page. Is there anything in principle
wrong with doing this? Will ASP.Net allow me to use an untethered renderer
in this fashoin?

I can figure all this out for myself, but I'd just like to know if anyone's
tried this before, if it's a bad idea to try in .Net, before I devote any
time to it.

Paul