A project I worked on suggests vibrating the bone just under the earlobe at around 50kHz with a piezoelectric stack might help. 8 years or so ago I helped make a pocket sized and rechargeable medical device that operates on this principle. Last I checked it was still in FDA hell but helping the majority of sufferers in the trials. The theory of operation is that is breaks up tiny air bubbles stuck to the hairs in the inner ear.

An interesting side note is that you could 'hear' a very high pitched sound when using the device even though 50kHz is far outside the standard human hearing range. We still are not sure but think we were hearing a lower harmonic of the tone bouncing around the skull.