you can use the http header insert function to insert the client ip address inside the http header when the CSM forwards clients to servers.
It is then up to you to retrieve this information on the server.
http://www.cisco.com/en/US/products/hw/switches/ps708/products_installation_and_configuration_guide_chapter09186a00802003ac.html#wp1047132
It is not recommended to try to turn on some logging on the CSM to get the list of connections.
You would kill the performance of the CSM.
If you don't want to get the info from the http header, then ask yourself why you only see the CSM address connecting to the servers.
Do you really need client nat ?
You should maybe change the design so client nat is not required and the CSM forwards client traffic unnated so the server can log exactly which client was connected.
Regards,
Gilles.