Found some FR-S goodies in the garage...
Two weighted shift knobs. Not sure about exact weight, but heavier than stock knob and both work well with OEM shifter (MT).
Individually: $25 (local pickup - Thurston Co.)
Buy both: $40 (local pickup - Thurston Co.)
https://photos.app.goo.gl/M7JuxmYBvI0OZHu23
https://photos.app.goo.gl/tV6xifVkXZpAYhLJ3
https://photos.app.goo.gl/8Xgq6SzBuT7Az0YR2