Accessing Box platform app as a managed user

Hi,

I have been trying to integrate box platform with a website. The use case is pretty simple-

1. End user comes to the website, uploads document
2. Document goes to box.com to a specific website owner's box account (stakeholder in the website). This user account will change for different forms. So if there are 10 different forms, there could be 10 different owners and each owner should get documents specific to his/her form. 
   
   Example- if form A belongs to stakeholder A, then the document submitted by an end-user should go to stakeholder A's box account but the end-user will never know where the document was stored.

For this, I used the box-platform to configure an App and completed all the steps mentioned at [1]. Everything works fine and I am able to upload files to an "App User's" account through my code by using the Box Java SDK.

But the problem is that an App user is not where the file should go to since these are not "real box user". The file should go to a managed user's account. That is, if i add a new user under https://app.box.com/master/users, I should be able to post the file to this user account, rather than an "App user's" account which has to be created programtically (as per my understanding).

Is there a way to post a file to a managed user's account through an App using the box platform? I tried changing the "User Type" of my App to "Standard box users" and then providing their login ID to generate oAuth token but that does not seem to work and the file upload fails.

I see in the docs "At this point in time, App Auth can only be used with App Users.", but I'm not convinced that this doesn't work.

Apologies if this has been asked before, but my search words were giving way too many results!

[1]- https://docs.box.com/v2.0/docs/configuring-box-platform 

Thanks!