Very interesting utility. I can think of a couple uses for something like this already. Note that your example didn't work as the file named starpage misspelled "example.php". Also should rename starpage to something that will automatically load like "index.html" or similar.
My test broke when sumitting a form that used a relative url and "get" instead of "post". Not sure which one was the problem though.
Is there any way to handle webpages that use flash? This didn't work for me either.