It is possible to use WhereScape RED parameters in a WHERE clause, even when the parameters screen is not displayed during procedure generation.
An example of this on SQL Server would be to have a parameter named param1 with a value of 1.
In your WHERE clause box you could enter
WHERE MyColumn = dbo.WsParameterReadF('param1')
WHERE MyColumn = (select WsParameterRead('param1') from dual)
Would achieve the same result.
You can find WsParameterRead and WsParameterReadF documented in the 'Callable Routines' section of the WhereScape RED User Guide.