Depends on the addin you are trying to utilize. You might be for example be able to launch the add-in using JSL, get a reference to the UI and press the button to run the query.
Most likely someone has done this before and also knows how to but not for the addin you have. If the add-in is using modal window, then it will be much more difficult or impossible (not 100% sure if you could bypass modality). Below is very simple example
Names Default To Here(1); New Window("Example", rb = Radio Box({"single", "double", "triple"}, Show(rb << Get())) ); wait(2); // for demo purposes wref = Window("Example"); wref[RadioBox(1)] << Set(2, Run Script(0));
Also what do you mean by this "...and don’t have access to script"? is the add-in script encrypted?