Maybe apply a MAC-based ACL on the concentrating switch to allow only Cisco MACs (the MAC of the AP Ethernet interface)?
I'm not sure (haven't tried it), but, worse case, setup an additiional VLAN (so you have a tag & trunk established), blackhole the Native VLAN, and I believe, the tagged frames from the AP can pass through the MAC-secured port.
Many of the SOHO APs cannot authenticate against RADIUS. Also, the RADIUS server must be configured to accept authentication requests from specific requesters.
If you're talking about someone plugging an AP into their PC jack, that's going to go back to creating a policy (the first step to any kind of security) - if a user gets caught, the user gets fired. If management can't accept implementing a policy like that, your company's problems are larger than a/some rogue access points (IMHO).
FWIW
Scott
Scott