Check out Amazon Business, which appears to allow you to set up multiple users in a hierarchy (including at least some sort of a custom "approvals" system), set thresholds, etc...
Not sure if it's new or not, recently got a call about getting into it though we declined as we're a small shop & already happy with the level of service we get via Prime.
http://www.amazon.com/b?node=11261610011
Not sure if it's new or not, recently got a call about getting into it though we declined as we're a small shop & already happy with the level of service we get via Prime.