Hey Jim,
Yes, it's certainly possible. Just register a "filetype", like .xyz, that is associated with your app. Then, when you generate a product key using LimeLM, instead of sending them a key, send them a file License.xyz that just contains the product key. When they double click the file, read the file in your app and use the TurboActivate CheckAndSavePKey() / Activate() functions.
In my opinion files are less convenient than a simple 30-ish character string.