Verified!
Mictester’s relay switching scheme for momentary NO switch, using Neutrik-style 6-pin jacks (like Tayda). Uses 40106 CMOS with transistors to trigger typical latching relay (AL5WK, etc). Resistors and sub-µF caps are 0805 surface mount.
No ground separation or opto muting; may allow audible pop with some circuits.
Note that the input jack is on the left when the component side is up. For RTL signal flow, you could mount the populated board with the components down and probably have room for pots above, in a 125b–but I haven’t tried it.

Verified!
Compact layout with bias brought out to a pot. Schematic is based on the ilovefuzz.com schematic, with a 25k pot replacing the 8k resistor at the collector of Q3. Transistor pinouts are all CBE with collectors closest to the pots. C6 is a tight fit behind the pot–not a good place for busting out the mojo!