Yes. Via CPL, it is possible to force the ProxySG to use HTTP/1.0 requests instead of 1.1. Using HTTP/1.0 will reduce performance but some applications do not support the new functionality of HTTP/1.1
Here is an example on how to force HTTP/1.0 responses to requests where the user-agent contains "blackberry"
<proxy>
request.header.user-agent="blackberry" http.response.version(1.0)