There could possibly be a simpler way to do this.
You could create a UCM partition containing translation patterns that translate the DTMF code to the PSTN number.
The CTI ports used by the UCCX application could access this partition in their CSS - no need for XML or Database.
Set your script to dial the entered DTMF code and it will be translated to the PSTN number
Would make it easy to add new DTMF - PSTN codes but maybe not too great on the CUCM front havng 200 translation patterns.
Just a thought