Microflow access to non-persistent entity with private data (no access rights)

We have some fields in our datamodel that can never be read by the user. This data is retrieved from another system before opening the page and we want to use this data in a microflow directly after the page. What is the best way of keeping this data? We created a non-persistent object with the private fields, that is separate from the main object, but connected via association. The problem is that we cannot seem to retrieve this object by microflow without adding ‘read’ access rights for the user. This is exactly what we don't want since this is private data. We don't persist any data in the app. Thanks in advance!