You can't use custom license features, but you can use the Web API. For instance you could put a simple script on your website to get the total & remaining activations for a key.
A simple way to do this is:
- Get the product key using the TurboActivate function GetPKey().
- POST this to a script on your website.
- The script will then use limelm.pkey.getID to turn the product key to a usable ID, then use this ID to get the remaining activations using limelm.pkey.getDetails.
Tell me if this helps.