Forgive me, but the term "stems" gets misused a lot, so for clarity:
If you mean "parts" (as in each track), you could try the Bounce Tracks macro here, which automates bouncing multiple tracks in one go.
If you actually mean "stems" (bounced subgroups of parts), then you can try the macro below, which automates part of the process of a single bounce.
Bounce Part-Stem.kmmacros (65 KB)
In Use:
Set up your stem bounce (track solos, etc.) and then hit ⌥⌘B to automate the bounce settings and auto-naming.
You will be prompted for a stem name, which will default to the name of the currently selected track (you'll see what I mean).
The macro ends at the Bounce dialog, so you can choose a destination folder and hit ↵ to start the bounce.