After scouring the release notes, it appears you should be able to update 
your client without cam cas. Here is a note under the UTF-8 section:

 If you only upgrade to the latest version of the Cisco NAC Agent, and 
leave your CAM/CAS at release 4.5(1) or earlier, the Agent operates as an 
English-only entity—you cannot take advantage of the native operating 
system localization support available to Cisco NAC Agent users who are 
logging in to a 4.6(1) CAM/CAS network. 

Although you lose the funtionaly of native language support it appears you 
should be able to successfully take on the new client without forcing a 
cam/cas update.