How Can I underclock My GPU by ALOT

[Fish Stickington]

I have used things like Gigabyte OC Guru, EVGA, MSI Afterburner, they all let me underclock my card but only by a bit, I want to underclock my GPU even more by probably 200MHz, probably more. Anybody know how to do this?

 

[JDB Computing]

Why do you want to?