So, this does not answer you specific issue. In your case, if you don't mind a
bit of wallboard repair, it is possible (we have done it), to very carefully cut a shallow groove in the wallboard, just wide and deep enough to accommodate the speaker wire. You will have to then cover the groove with wallboard joint compound and repaint. This is not as drastic as pulling off the drywall, but, it does require some patching.
Good luck