Checks for local files in wp-content/uploads and rewrites the URL to the live server if needed. Also checks that the HOST is local, so it won't run outside of your dev URL.

.htaccess (upload files from proxy)

// Place this BEFORE the WordPress Rewrite rules
// Be sure to edit LOCALHOST and LIVESITE with the proper URL's

<IfModule mod_rewrite.c>
	RewriteEngine On
	RewriteBase /wp-content/uploads/
	RewriteCond %{HTTP_HOST} ^LOCALHOST\.dev$ [NC]  
	RewriteCond %{REQUEST_URI} ^/wp-content/uploads/
	RewriteCond %{REQUEST_FILENAME} !-d
	RewriteCond %{REQUEST_FILENAME} !-f
	RewriteRule ^(.*)$ http://LIVESITE.com/$1 [R,L,NC]
</IfModule>

Just used this. It is sweet!!!