Having a use-case where you on-demand must bring in assets to a host application? We have a concept called Unified DAM UI which is a UI that comes with your Media Manager 5 (from 5.5.4).
It can be easily embedded into any host application as an iframe which can then listen on asset selection. Basically, you will be getting an asset id and asset URL which can then be uploaded directly into your host application.
Please have a look at: