Users Loop Orderby Multiple Fields?

I need to display an alphabatized list of users. I want to sort by the field company_name but several of the members have no company name listed. In the case of those users, I want to sort by first name. Ideally, I could user something like

[users role=member orderby=user_fields user_fields=company_name,first_name order=ASC]

but that doesn’t work. Is there some way I can accomplish this?

Thanks in advance!