I don't think that feature is available. I know there will be a business reason behind, just curious to know why would you want such a feature?
I am not sure what you meant by optional RTP. Your script would be referencing both the RTPS. If one is optional, what would the script looks like if a value is not given in Planning?
(Your script can have more than one RTP. When you launch them in Planning, the script is scanned for all the RTPs and are prompted for values. Once the values are given (assuming nothing is set to hidden), then the script is regenerated by replacing all the refrences of RTPs with their value.). So as Celcin said, what is the use case here?