I wouldn't bother trying to 'trick' it into digital. You would have to modify the CPS to allow you to use an entitlement you didn't purchase which would be illegal.
It can be done but good luck finding it, moto would be none to happy to see that anywhere online.
However, if you do go the legitimate route.. put the entitlement in there BEFORE you upgrade the firmware.
If you upgrade the firmware first, it'll be stuck as an analog radio and while it will take the entitlement it won't actually switch over without another firmware update. Which you can't do if you updated to the latest.
That issue may have been fixed at this point but I'm not sure, had to send 3 back to the depot for repair after this happened during a switch over of 100 radios or so.