Searching by User ID

Hi all, i’m trying to work out how allow users to search by user ID. Users obviously have an underlying ID - I can see this in:

http://mysite/User/Summary.html?id=1234

And this happily shows me details of the user in question etc etc etc. What I can’t see how to do, is use this number for searching. For example - searching in the “quick search” or the “User search” box does not look at this field. Searching for:

Owner = 1234

also doesn’t work, whereas
Owner = ‘Bob@somewhere.com’

does.

The reason I’m asking, is I’m trying to model a scenario for a customer, where they have trained all of their customers to use / refer to their “Customer number”. I’d like the workflow to be as easy as possible - so customer service agent can simply type the number in a box and get back the matching record.

Any tips for how to either modify a template (which one?) and what are the object names I should be referring to? (Owner.Id or ???)

FWIW I can’t seem to search and return “OwnerId OwnerID Owner.ID” and other variants of the same theme either. I can return “OwnerName” just fine however.