On the backside of the Panasonic WM61A omni directional, and the Panasonic WM55-A103 uni-directional back electrets capsules, the source of the internal FET is directly connected to the housing via a mass connection from one soldering island to the rim (P1).

The source has to become isolated from mass. Isolate that island from mass by scratching the mass connection.

The now isolated island becomes the newly created low-Z audio output (P2) and must be connected to R2.

The other soldering island remains the already existing high-Z drain output (P3) and will be connected to R1.