I am implementing UCES (UCES = Biller Direct + ISU functionality). According to Biller Direct Modification documentation (http://help.sap.com/saphelp_erp2005vp/helpdata/en/05/8d763ee8f9e946e10000000a114084/frameset.htm) (under Integrating Separate Customer Functions),
"The SAP Biller Direct delivery contains example code for customer-defined enhancements in the .ear file that you can use as template for implementing your own functions. After you have unpacked the application as set out in the implementation guide, you can find folder \docs\customerExtensions. "
The ear file or example should have CustomerExtendAction.java, CustomerExtendRootBean.java, CustomerExtendDataBean.java and etc files.
I don't have these files in \docs\customerExtensions folder.
Please send a copy to me if you have it. My email is email@example.com