It might be quite an interesting project to write a little script which reads through all your pages andnthen it finds a link with variables in the url it locates that files and replaces all references to that variable in that file with $_GET['varname'] and the same for forms and POST/GET.
Now to avoid lots of debuging you're going to have to do some pretty funky stuff like checking if the variable is in a string for one, and also checking if the variable is in a function and if so, if the variable has been made global before the point of it being used in the function.
Note: If you're only dealling with a small app it may be easier and quicker to do this by hand, however you'll miss out on all the fun :p
Goo luck,
and don't forget to call if you get lost 🙂
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