Hide-a-Holster would work or Secure-it/ Secure-it Holsters. Is it a moldable polymer to fit/adjust to any area? I really enjoy the decibullz ear buds due to their moldable polymer which allows any user to perfectly fit your ear. Would have a lot of interested people in your idea if you could make a ratchet or click in feature for your current holster to slide into a molded shell as a retainer. Unless you went to the junk yard and made templates from broke vehicles for the door compartments.