If THIS_IS_THE_PART_THAT_I_NEED is just a set of values, you might create one page for each value and use page-property 'url’ to make the page available with https://myapp.mendixcloud.com/p/THIS_IS_THE_PART_I_NEED/<Dataview-objectid>
I think you have 2 options:
1) Extend your URL so you have just one configured deeplink:
That way, you’ll have the full path you need in the microflow.
2) Change the Deeplink module
Edit the java code that calls the deep link microflow, and add the additional parameter