OK, after some more thorough forum searching, I found the following thread:
http://forum.java.sun.com/thread.jspa?forumID=23&threadID=654224
Summary:
- /send response goes in a special (undocumented!) variable called ${response}
- /send takes a second parameter which is the expected response
Hope that saves someone else some time. I think it is rediculous that these basic features are not properly documented in the JCOP tools.