You can add following parameter to http and https transport receivers of WSO2 ESB .
<parameter name="WSDLEPRPrefix" locked="false">[load-balancer-url]</parameter>
For example:
<parameter name="WSDLEPRPrefix" locked="false">http://esb.cloud-test.wso2.com:8280</parameter>
You need to edit following file. <WSO2-ESB-HOME>repository/conf/axis2/axis2.xml
This step is necessary for configuring WSO2 ELB also. See following ELB doc for more information.
http://docs.wso2.org/wiki/pages/viewpage.action?pageId=26839403