1
Add Armature
Select the object with the shape key animation and press shift + A
2
Add Single Bone
Go to, armature and add a single bone
This drops the bone in hierarchy, but it’s not connected to the object
3
Select Both Objects
Select both, the object and the armature (bone), first select the armature, then the object
4
Parent Objects
Then press command + P to parent
5
Choose Automatic Weights
Select ‘with automatic weights’
6
Export Settings
For export select the armature in the hierarchy and choose ‘Selected Objects’ under Include ‘Limit to’ in the export settings.