As far as I can see there has only been one way added for importing custom art using Unity. this post is to give another way to add custom art and models to the imports for Oculus without using unity.
What you will need: Paint 3D
Open a new paint 3D Click 3D shapes tab and place a new cube Stretch cube to desired size, and flip and flatten the cube to look like a basic canvas. Click on stickers tab and add new sticker from picture library Place sticker on the front of the new flat cube, and click the green check save the new model to your Oculus home imports in Documents as a 3D model GLB file Load up Oculus and place your new poster.