Post cache substitute a rendered action result

Question

I was wondering if it's possible to take the rendered content of an Action in ASP.NET MVC 1 and output it to a page via post-cache substitution.

I know it's possible to use an AJAX request however I'm trying to this on the page render.

Also, if you try to use Html.Substitute and use RenderAction from MVC Futures it throws an exception deep in MVC. It's expecting a Path/Url to be there, and one isn't thusly throwing an NRE.