I'm Dee from the TM4J team at Adaptavist. Good question!
While it's not possible to display the TM4J test cases directly in the structure, if you were to select an issue in the structure, you'll be able to see the covering tests in the "issue glance" (the side panel displaying the issue alongside Structure).
You may, however, be able to achieve more than this with ScriptRunner and Structure together. ScriptRunner allows you to customise Jira in many ways, you can see some examples of how this works alongside Structure here: https://library.adaptavist.com/collection/scriptrunner-structure