how to send http header over soap by specify "Accept-Encoding" ?   

I'm using SOAP toolkit 3.0 to make a request to web-service, and I want to 
know how to add more http header info. I want to add "Accept-Encoding: gzip" 
into http header but I cannot find any API to do. I use "HttpConnector30".
Thanks for your help.

date: Fri, 17 Aug 2007 05:34:01 -0700   author:   atanai