How to trick a page into running at a location different from it'sphysical location?

I have an application with a web page that I would like to run as if it
were at a different location than it actually resides at. As an example:

Imagine that I have a site layout as,

~/
~/foo/
~/foo/bar/

Web.config files exist at

~/web.config
~/foo/web.config
~/foo/bar/web.config

I have a web page

~/default.aspx

If someone comes along an requests page

~/foo/bar/default.aspx

I would like the request to be handled by ~/default.aspx, but as if it
were located at ~/foo/bar/default.aspx, importantly, I want all of the
inherited web.config information to reflect the ~/foo/bar/ path
hierarchy. I also want page-relative links to resolve based at ~/foo/bar.

I can't rewrite the path via RewritePath because the framework executes
~/default.aspx as if it is at ~/default.aspx, and I can't redirect the
client or server.transfer for the same reason.

I have written a custom IHttpHandlerFactory that handles determining the
correct page to load for each request (not precisely url rewriting but
similar), but I can't figure out how to get the page to load as if it is
at the requested url.

Essentially, my factory looks like this:

string newPath = DetermineNewPathForRequest(context);
return PageParser.GetCompiledPageInstance(newPath,
HostingEnvironment.MapPath(newPath), context);

This almost works. Page relative links resolve correctly, and custom
configuration sections that I've written respond to
WebConfigurationManager.GetSection calls correctly, but built-on
configuration sections don't get the inherited data.

For instance, if I define

~/web.config <- <pages masterPageFile="default" theme="default" />
~/foo/web.config <- <pages masterPageFile="foo" theme="foo" />
~/foo/bar/web.config <- <pages masterPageFile="bar" theme="bar" />

requesting ~/default.aspx, ~/foo/default.aspx, or ~/foo/bar/default.aspx
always returns a page with the default theme and master file, rather
than default.aspx customized with the appropriate theme/master set by
the execution directory's web.config, even though my factory doesn't
redirect, just loads the page directly.

This disparity between the automatic configuration sections and the
custom sections returned from WebConfigurationManager.GetSection really
confuses me. Does anyone know if I'm running into a bug, or is there
something about PageParser.GetCompiledPageInstance that I don't understand.

Thanks in advance, and sorry for the long post,
Luke