I am sure someone else can do this more elegantly but here is one method using vbscript.
Paste this into a .vbs file on a windows computer.
'Create the JMP application object
set jmp = Wscript.CreateObject("JMP.Application")
'Open a data table that already contains your script
set jmpdoc = jmp.OpenDocument("C:/test.jmp")
'Make it visible for demo
jmpdoc.Visible = True
'Set a table variable to be your 'parameter'
jmp.RunCommand("current data table() << Set Table Variable( ""input"", 20); ")
'Run the script
jmp.RunCommand("eval(Current Data Table() << Get Table Property( ""add Column"" ));")
Then make a data table called test.jmp in your C drive with a saved script called "add Column" that contains this:
dt = current data table();
val = dt << Get Table Variable("input");
New Column( "Column 2",
Numeric,
"Continuous",
Format( "Best", 12 ),
Values( {val, val, val} )
);
Double click the vbs file and you should see a new column with three rows set to 20.