Resolution:
BW Service and SOAPEventSource do not support HTTP Get Request as of the BW 5.6.2 release. In the SOAP V1.2 specification it states that "HTTTP binding with the SOAP Response message exchange pattern is restricted to the HTTP GET method. ... HTTP binding with the SOAP Request-Response message exchange pattern is restricted to the HTTP POST method..."

 A workaround is to use the HTTPReceiver and Serivce/SOAP EventSource. Attached is a sample BW project for reference (Filename:SOAP_OVER_HTTP_GET.zip). It uses a BW 5.6.x activity Invoke Partner for the local SOAP call. For BW 5.4.x and earlier, modify the project with SOAP R/R activity.