Possible to hack WP user IDs?

Hi all,

As you know WP users are assigned a default user ID (1, 2, 3, etc…). For our needs however, we would like our users to have a 6 digit user ID (000001, 000002, 000003, etc…). Is there some way to do this? I’ve been searching for a plugin but haven’t found one to date. I’m almost thinking it would have to be hacked.

Any help is appreciated, thank you!