Looking at the the Inheritance-Tree of TSQLScript and its Methods and Properties, i think it's the wrong "tool" (Component) to use with Parameters.
1) TSQLScript is not returning a Result (Like for a SELECT)
2) It uses the Execute(Direct)-Method of its Database/Connection-Object, which in itself should only be used for non-Result Statements
i Think TSQLScript is useful for, say, reimporting a SQLDump.
All said: If you have (to use) Parameters, use TSQLQuery. Period!
Or as you said: Stored procedures if the DBMS supports it
EDIT: I was just reading that Link.
If you need help with registering your own Procedure/Function give a shout