Prepopulating with other fields than the id

Is it possible to pre-populate using fields other than nid or uid?

The field we want to use is a long random text field.

It's for an entity form emailed out to anonymous users and we don't want the possibility for them to change the reference query to another entity.

We can search for the random field if we use an autocomplete field but not if we try to pre-populated from the url