One of my Crystal tricks is to add the option field from the master as a "subreport link". Right click the subreport and select "Change Subreport LInks..."
Then - go into the subreport and go into the Report-->Select Formulas-->Records...
Then remove the added subreport links. The variables will remain in the subreport and you can use them in any and all formulas - record selection and all others.
DaveO