You can simply use "Execute Script" operation in Workbench and make use of java.net.URL. Below links should help :
http://www.mkyong.com/webservices/jax-rs/restfull-java-client-with-java-net-url/
http://www.adobe.com/devnet/livecycle/articles/building-xml.html
http://help.adobe.com/en_US/livecycle/9.0/workbenchHelp/help.htm?content=000581.html
Hope this helps.
-Wasil