Looks like I've solved it.
Inside the database Command, we must declare a variable, edit it (add characters), and then use the variable in the SP call.
For ex.
declare @word varchar(20)
select @word = 'aaa' & '{?MY_PARAM}'
exec sp_MyProc @param1 = @word
A parameter of a stored procedure cannot be edited directly.
Edited by pl80 - 28 Nov 2012 at 3:07am