How can we add a Legal dictionary to the OWA spell check?

The OWA spell check searches a default dictionary which cannot be updated by the user.

To add a legal dictionary, a third-party add-on is required such as the one from Messageware (www.messageware.com). The Messageware Plus Pack includes Medical, Legal and Corporate dictionaries and allows users to add common terms, such as their last name to their personal roaming dictionary.