$> vi /spring-framework-3.0.0.CI-167/projects/spring-build/lib/ivy/jets3t.properties
then
#...
httpclient.proxy-autodetect=false
httpclient.proxy-host=<your-proxy-host>
httpclient.proxy-port=<your-proxy-port>
#...
This should proxy out any request (to s3). Note that proxy-autodetect is by default true.
You can now build the framework via ant:
/spring-framework-3.0.0.CI-167/projects/build-spring-framework$ ant