Unfortunately Unity doesn't provide a runtime OBJ importer. The closest thing they provide are Asset Bundles, but they require additional processing, which, as you've said, is not what you're looking for.
Alternatively, you can look in the Unity Asset Store for plugins that would provide this functionality. Here are two examples that are free of charge: Runtime OBJ Importer and OBJ Mesh IO. Please keep in mind that I did not personally test them and I cannot guarantee that they will work. They are just some examples of what you can expect to find.
We are developing an inventory app (Wikitude + Unity) for a client, which loads machine parts that are customised by hand.
They have purchased a 3D handheld scanner and the scanner is used to scan the model with texture and software exports to OBJ, optimised, to scale and correct standard orientation.
When staff launches the app, they will be offered a catalogue of categories, and within each category, a list of parts which they can tap to load (over the air) into the app and display in AR view (much like IKEA app).
They want a seamless way of loading their scanned 3D model directly to some CMS (with thumbnail image) without having another layer of process e.g. us converting the files or adjusting and uploading the files etc.
What other ways can we do this from a platform point of view?