Dependent UDFs

Here is what I am trying to do:

basically UDF # 1 will have options A, B, and C.  UDF # will have options A through Z.  If opton A is selected in UDF #1 then the user will be able to select A-D in UDF #2, if option B is selected in UDF #1 then user will be able to select E-P in UDF#2,  etc

Any suggestions on how to do this in Sage ERP 100 Premium 5.30.1.0

Thanks
Brian