You can use "Move Selected Columns()" to move a column that you have added to the end of your data table. However, just as with the "Add Multiple Columns" the choices are focused on adding after a column. So you would have to subtract 1 from your position, and then use that value as the insert position
Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << New Column("The New Column", set selected)
Wait( 2 );
dt << Move Selected Columns( after(as column(1)) );
// or
Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
dt << Add Multiple Columns( "Added ", 2, after(as column(1)), numeric );
Jim