I think I *may* know a way to do it.
You will need 2 general purpose diodes from radioshack. These diodes have 2 leads, and one side of the diode has black other side has orange. Solder the orange side of the diode to the positive portion of the headphone jack. Do this again using another diode onto the negative portion of the headphone jack. Now solder the black ends of the positive and negative diodes proper points of the lm386/LEDs respectively.