Is it possible to store the plain buffer data in gltf files?
Embedding human readable data is not supported. However you can put the data into a data uri to store the data inline in base64 format.

"buffers": {
    "a-buffer-id": {
        "byteLength": 1024,
        "type": "arraybuffer",
        "uri"="data:application/octet-stream;base64,..."
    }
},