No, you are not the first one
On a branch 1 we have already an initial implementation of the timer event listeners but there are some aspects still missing.
In 7.6 we implemented
VariableOnPart 2, which is a custom extension element. The
VariableOnPart can be used inside sentries, which would mean, that when a variable does a specific transition (create, update or delete), then this variable specified
VariableOnPart gets fulfilled.
Maybe you can use this as a workaround. So whenever the external document is received, a case instance variable is created and added to the case instance. This would trigger the
VariableOnPart, so that the entry criterion of the human task is fired.