Auto-Fill Form Script

I want to be able to fill in an online form that I don't control. It's HTML but has no javascript installed to allow it to accept variables from a POST or GET statement. I will be using this form hundreds of times, so to be able to fill in the form automatically would be great. The data will change, so I don't think roboform or other form filler app will work. If Greasemonkey will do it, that's fine... but I need to be able to process a form of my own that will send all the variables and values to some sort of processor that then will fill the target form.