I have 2 pieces of my puzzle:
1) a no-Grails project named core-module with standalone GORM:
dependencies {
compile \'org.grails:grails-da
Grails only scans packages in the application by default for performance reasons. Override limitScanningToApplication() to return false in your Application class and define the packages you wish to scan by overriding packageNames() in your Application class.
Grails will then automatically discover the Mongo GORM classes