How can I redirect one URL to another (including subdirectories) without changing the URL in address bar (so something like mod_rewrite features)?

In a mod_rewrite, if the rewriterule result contains an external URL such as http://www.example.com/$1 then it actually redirects instead of rewriting, because the result URL must be internal for it to work normally.

What I want is basically explained in my topic - How can I redirect one URL to another (including subdirectories) without changing the URL in address bar (so something like mod_rewrite features)?

I heard about using ProxyPass but am afraid of how to use it, implement it, etc.

So any suggestions that might help?

If it helps, then this is what I have right now in my mod_rewrite (and it achieves exactly what I want, except that it redirects and does not keep the original URL in address bar.)

.HTACCESS CONTENT (in http://blog.kinggary.com/ ):
RewriteRule ^(.*)$ http://gary.blogs.com/$1