Grouping users in the context of the company

Hello,
I'm trying to build community for customers,
single customer may have a dozen or several dozen members,
how can I group them to see the company context in admin panel?

I had considered to use:
- groups - but it's non optimal to create so many of them, because groups have individual permissions per each forums
- custom ranks - but it's not practical, especially I don't want common members to see the company context of others
- custom fields - sound's most reasonable, unfortunately I can not show this field on the user list in admin panel

any better ideas?