It's not possible to get only the passed property fields for output:

— BEGIN SHELL —

[foo@example ~]$ ./issue.sh
HTTP/1.1 200 OK
Date: Tue, 04 Feb 2014 15:38:05 GMT
Server: Apache
X-Powered-By: PHP/5.3.3
Vary: Accept-Encoding,User-Agent
Content-Length: 225
Content-Type: application/json

{"jsonrpc":"2.0","result":[

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

,

{"itemid":"23299"}

],"id":1}

— END SHELL —

Is this the expected behavior? I'm pretty sure to have used the "output" parameter this way with a different api method successfully.