TPAI should be present in the Export menu of the context menu for a photo in Lightoom.
Currently TPAI for DNG file production is present only in the File > Plug-in Extras menu, which is not an obvious or user-friendly place for it.
I would note that DxO PureRAW and Helicon Focus are both in the Export menu and operate on raw files perfectly fine. Helicon even lists both TIFF and DNG options in the Export menu.
