How can I send "processInstanceId" when signaling a BPM service in FSW?

Issue

I am trying to signal an event into an ongoing jBPM process instance but I don't know how I can do it without using SOAP.
It seems to be fairly straight-forward when you use SOAP, but I want to use SCA binding. SOAP is too much overhead in this case where the signal is sent from another SwitchYard application.
How can I signal a running process instance using SCA binding instead of SOAP binding? My understanding is that you have to put the following fields in the SOAP header when you use SOAP:
```
<soap:Header>  
    <bpm:processInstanceId>1</bpm:processInstanceId>  
    <bpm:processEvent>Hello World</bpm:processEvent> 
</soap:Header>
```
Based on these fields SwitchYard / jBPM will then know which process instance to signal. How can I set the process instance ID when using SCA binding?

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