Its simple.
Whichever WSDL you have used for the intermediate event in the sub-process, use the same WSDL in an automated activity in the parent process.
Please keep in mind that the correlation condition used in the intermediate event should be same as the input mapping of the automated activity. For example,
Correlation condition of intermediate event: NewOperation/Variable1=ProcessContext/Variable1
Input mapping of automated activity: Process Context to 'NewOperation/Variable1' with same value.
For example, the part of the main process will look like this:
(The branches going down will meet at the parallel join)
The sub-process will look like this:
Correlation condition of intermediate event:
NewOperation/Variable1=concat(ProcessContext/Variable1,"abc")
Input Mapping of Automated Activty will flow from Process Context/Variable1 to NewOperation/Variable1. In the expression editor for NewOperation/Variable1, write the function:
concat(ProcessContext/Variable1,"abc")
What this will do is, since the WSDL and the condition for tboth, the automated activity as well as the intermediate event is the same, they will mutually trigger each other.
Note: This is only to put back the process execution back to the parent process. You will have to modify the process design accordingly.
I have implemented this in a scenario and it works fine.
Hope it helps.