Arjan,
I may not completely understand what you are trying to accomplish, but if you have a grid containing Customer objects, you can display the Orders associated with a selected Customer without using a microflow. To do this:
When you open this page, it will show a list of Orders associated with the selected customer.
One note: you can also do this by creating a Dataview on the original page whose datasource is listen to grid. Chose the customer datagrid as the source. Inside of this dataview, create a grid that displays Orders associated with the customer.
Hope that helps,
Mike
In the meantime I found some information in a blog post related to this subject. See below microflow for a working solution to my problem. In case there are other or better solutions, I would be glad to hear about it.