Your reply was a little ambigious but judging from what you want, why don't you let PHP write the coldfusion form out for you with your variables already set?
Assuming that your PHP form properly intercepts the variables and modifies them, why don't you overwrite the original coldfusion form with another coldfusion type file written by PHP?
PHP->intercepts form variables
PHP writes a file called "myform.cfml" (coldfusion page) with the form variables intercepted
when customer requests myform.cfml they don't know how that was generated nor do they care--to them its just a cold fusion page, but underneath this particular form was actually written by the underlying PHP script.
I really still don't understand what you want to do. That's the best I can do based on your info. I hope that helps.
jm