You could try to use the community commons executeMicroflowAsUser. This way you could use a microflow and open a page as that user. Problem is that you know beforehand which pages you want to open as that user.
But it would not be the same as login in as that user. That would in my opinion almost be impossible to achieve since you have to know the password of that user. But you can always download the backup of the data and debug locally as that user. Then you could do everything as that user and talk the user to the problem since your local database is the same as the cloud database.
Regards,
Ronald