Most blue tooth speakers, and most devices in general, are designed to fit as much as possible inside of the devices outer shell, that way it has the most capability possible while keeping the production costs down. I would think it unlikely that the speaker would have much room to allow for a external passive radiator to be installed. However I know some desktop speakers leave room in the form of bass ducts to improve bass, in my experience blue tooth speakers are different. There is always a chance there is room, but it would be hard to know without opening one up and looking at the internals.
First thing I usually check when I am experiencing difficulties with any repair is how the part looks to be secured. Check if it looks like there is adhesive or if there is small screws. Obviously both would prevent you from removing the vibrators. I will assume there are no screws because it should be obvious is there is. Again assuming it is adhesive the easiest way to soften/weaken the adhesive is using isopropyl alcohol. This should break down the glue enough to allow you to carefully pry the vibrators out. You can use a spudger if you have one, if not a small flat head screwdriver and make sure not to pry on any points that could break off (like in between the body and rotating weight) but rather somewhere like the main body (the larger, metal section) of the vibrator. Hope that helps!
From my experience the only way to fix this issue is to replace the display, that includes the LCD and Digitizer. I have found this is a fairly complicated repair if you do not know what you are doing and I would recommend getting it repaired by a professional.