If a WS has multiple operations and if you want to invoke a particular operation from a BPEL invoke activity, the process is no different than invoking a simple WS with one operation.
- Create an external reference for the WS by drag/dropping the WebService component from the component pallete to the SOA Composite and select the wsdl of the appropriate WS. I assume the WS is already deployed.
- Create a BPEL process and create a wire between the BPEL and the WS.
- With this, a partner link is created in the .bpel file.
- Create an invoke activity in the BPEL process and wire to the partner link. In the Edit Invoke popup, under the partner role, you can find the operation dropdown from which you select the appropriate operation. Based on the operation selected, the variable gets created(just in case you opt to automatically create a new one).