The customer I do this for has this enabled in their Application Record:
Online synchronisation capability YES
Offline synchronisation capability YES
Offline license download capability YES
I just click on Download License Keys, and it gives me a warning:
Downloading the license key will permanently attach these products to this application record. After clicking 'commit' you will not be able to remove these licenses from this record. If you are unsure about this action, please consult the online help (Online vs Offline Activation) or contact your support representative.
It then takes you to a page that I print to pdf which includes a license key. On the controller, go into the license area and click Change. Adjust the number of licenses to what you have now in AMC, and then type in the license key.
I've only been working with the Mitel for less than 12 months, and this was what I was shown by my predecessor. I didn't know it shouldn't work.