You could raise a requirement here to try to get the property added:
http://www.ibm.com/developerworks/rfe/?PROD_ID=532
It is almost certainly jsut an oversight, but, given that 6.1 is almost out of support you may find that an RFE will not be accepted, or even if it is it will be targeted to a future release.
The embedded EG level listener outputs it's URI registrations with the following command:
mqsireportproperties -e -o HTTP(S)Connector -r
So if you could temporarily swith the http nodes to use the EG level listener using:
mqsichangeproeprties -e -o ExecutionGroup -n httpNodesUseEmbeddedListener -v true
Then mqsireportproperties will give you what you need.
Otherwise I think the best bet is writing a small CMP app that examines the flows that are deployed looking for SOAP and HTTP Input Nodes and extract the property that way.