Indeed, the image is JPEG encoded. I am not sure how difficult it would be to implement. It could be if it is just like one JPEG file put into the TIFF file. It seems you can use another encoding, so you're not stuck?
To explore the various images, instantiate explicitly a TBGRAReadTiff (of BGRAReadTiff unit) and call LoadFromStream function.
Then you have ImageCount and Images properties. For example reader.Images[0].Img as TBGRABitmap will be the first image.