Is this point of the stored procedure to avoid writing a statement each time? If so, would it suffice to use EXECUTE IMMEDIATE within the stored procedure?

I.e.

CREATE PROCEDURE abc.MyTableSelect (
  IN @VariableName CHAR(128)
)
RESULT (
  A INTEGER,
  B INTEGER,
  C INTEGER
)
BEGIN
  EXECUTE IMMEDIATE WITH RESULT SET ON
     'SELECT A, B, C FROM MyTable
      ORDER BY ' || @VariableName;
END;

You can also use a case statement in the order by clause, something like this:

CREATE PROCEDURE abc.MyTableSelect (
   IN @VariableName CHAR(128)
)
RESULT (
  A INTEGER,
  B INTEGER,
  C INTEGER
)
BEGIN
  SELECT A, B, C FROM MyTable
      ORDER BY case @VariableName 
         when 'A' then A
         when 'B' then B
         when 'C' then C
      end case asc;
END;

FWIW, with V17 you can do that without EXECUTE IMMEDIATE - namely with the help of the newly introduced indirect identifiers.

Here's a small sample with a stored procedure that will query the system catalog and return a result set with owner, table and column names and ids ordered by two columns as specified by means of the procedure's arguments.

Instead of using EXECUTE IMMEDIATE, the statement is parametrized with the particular '[Variablename]' syntax and therefore is much easier to write, read and maintain.

create or replace procedure STP_SysCatalogOrderedBy(in @SortByColumnName1 char(128), in @SortByColumnName2 char(128))
begin
    select user_name, creator, table_name, ST.table_id, table_type,
       column_name, column_id
    from sys.sysuser SU key join sys.systab ST key join sys.systabcol SC
        key join sys.sysuserlist
    order by `[@SortByColumnName1]`, `[@SortByColumnName2]`;
end;

-- some possible calls
call STP_SysCatalogOrderedBy('table_name', 'column_id');
call STP_SysCatalogOrderedBy('column_name', 'table_name');
call STP_SysCatalogOrderedBy('user_name', 'table_name');

-- Note, here both variables must be specified and must be valid column names:

-- Will fail with SQLCODE -1722 ("The variable '@SortByColumnName2' must not be NULL in this context")
call STP_SysCatalogOrderedBy('user_name', null);
 -- will fail with SQLCODE -143 ("Column '' not found')
call STP_SysCatalogOrderedBy('user_name', '')

I guess but am not sure that such predicates should be sargable (see Glenn's original reply).

A big thanks to Michael Fischer for sharing that insight at the German SQL Anywhere Developer Day:)