Include custom field in simple search?

Hi all,
How can I make our RT’s simple search include a certain custom field by default, but not error out if that field doesn’t apply to a user’s allowed queues?

We have RT to help us keep track of orders which customers complain about, thus each ticket has a custom field for the order number. Needless to say, it would be very helpful for us to be able to easily search tickets by order number. Users don’t want to have to type

Cf.“Order Number”:[number]

each time. Can I make RT include this CF in simple searches by default? Or use a special symbol to denote this field? The only problem might be that this field doesn’t apply to all tickets, so the search would have to ignore it for any queue whose tickets don’t have an order number field.

Thanks for any suggestions.