Spent too long trying to figure this out, but the readme example of a DBus call does not import values at all.
The non-functional example in the readme is
[keys.action]
  [dbus]
    object = "object"
    path = "path"
    method = "method"
    value = "value"
 
In order to make it work, dbus must be added to the keys.action
[keys.action.dbus]
    object = "object"
    path = "path"
    method = "method"
    value = "value"
 
I've confirmed this works, at least for session bus calls, on 0.9.0. Will submit a change to readme to clear up confusion