This is actually already implemented:

curl -i -v "http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo/cars?limit=5&offset=0&color=red&qmx=bigboss"
* About to connect() to controllerdemo-danbev.rhcloud.com port 80 (#0)
*   Trying 50.17.128.13...
* connected
* Connected to controllerdemo-danbev.rhcloud.com (50.17.128.13) port 80 (#0)
> GET /aerogear-controller-demo/cars?limit=5&offset=0&color=red&qmx=bigboss HTTP/1.1
> User-Agent: curl/7.24.0 (x86_64-apple-darwin12.0) libcurl/7.24.0 OpenSSL/0.9.8r zlib/1.2.5
> Host: controllerdemo-danbev.rhcloud.com
> Accept: */*
> 
< HTTP/1.1 200 OK
HTTP/1.1 200 OK
< Date: Wed, 23 Jan 2013 18:06:07 GMT
Date: Wed, 23 Jan 2013 18:06:07 GMT
< Server: Apache-Coyote/1.1
Server: Apache-Coyote/1.1
< Link: <http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo/cars?limit=5&offset=5&color=red&qmx=bigboss>; rel="next"
Link: <http://controllerdemo-danbev.rhcloud.com/aerogear-controller-demo/cars?limit=5&offset=5&color=red&qmx=bigboss>; rel="next"
< Content-Type: application/custom;charset=UTF-8
Content-Type: application/custom;charset=UTF-8
< Content-Length: 228
Content-Length: 228
< Vary: Accept-Encoding
Vary: Accept-Encoding
< Strict-Transport-Security: max-age=15768000, includeSubDomains
Strict-Transport-Security: max-age=15768000, includeSubDomains

< 
* Connection #0 to host controllerdemo-danbev.rhcloud.com left intact
CustomMediaTypeResponder returned: [Car[id='6'color='red', brand='Audi'], Car[id='13'color='red', brand='BMW'], Car[id='20'color='red', brand='Fiat'], Car[id='27'color='red', brand='Golf'], Car[id='34'color='red', brand='Lada']]* Closing connection #0

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