Get Message Header ID in Business Process

I'm looking for a way to get the message header ID for the current message in a Request to a Business Process.

I've located some code that gives me what I need, but it runs the risk of violating the "abstraction layer" ISC has in place around such things. And while I very much appreciate their efforts at keeping things simple for me ... well, sometimes you just have to dig through the guts to get what you want.

Is there a documented, deprecation-resistant method for getting at %Ensemble("%Process").%PrimaryRequestHeader.%Id() from within a  BP?