Register Users 'x' months after the completion of another activity

Register Users: If you have two courses e.g. Fire Awareness and Fire Awareness Refresher it would be super useful to be able to register users on to the Refresher 'x' months after the completion of Fire Awareness.

At present you'd have to register a user on to both and set a far flung due date which wouldnt necessarily correlate with when its actually required to be completed, plus they'll have an activity that they can access but are not required to do yet.