There is an easy way to insert steps to invoke services that are not listed in Developer.
Insert an invoke step to call any arbitrary service, like pub.string:concat.
Select the step then on the properties pane, edit the service name to be the service that you want to call. E.g. replace pub.string:concat with wm.art.admin.connection:getResourceConfiguration.
The editor pane will update to show the inputs/outputs of the desired service, if they are declared (for example, many WmRoot services do not declare inputs/outputs though they expect particular pipeline vars to be present).
HTH
#Adapters-and-E-Standards#webMethods#Integration-Server-and-ESB