Microchip IS1678S Questions - wanting to implement SPP as simply as possible
To help anyone else in the future grappling with this, you can use the IS1678S exactly as I wish without any need for a host stack. I got this going with the BM78 module which uses the IS1678S. I had to change the RF channel to make it easy to connect up to my Linux laptop's rfcomm port, but that was easy with the UI tool. 

Mictrochip have confirmed that no external stack at all is needed when switching from module to SoC, so this is a very good solution.