There are many modellers that wish to manual uncouple with a small tool and Kadee® offers the #241 "Dual Tool" manual uncoupler and spring pick combination.
For manual uncoupling the 118 "SF" shelf coupler the #241 has a "pointed" end to fit around the top shelf. The other "blade" end of the #241 is for standard couplers, also, the blade end has nubs so it can double as a spring pick for inserting small coil springs.
To manual uncouple the #118 coupler with the pointed end of the #241 "Dual Tool", first push the cars together where the coupler knuckles compress against each other, insert the pointed end against the "outside" of the hooked tip of the knuckle as illustrated (the knuckle is the moving part of the coupler head).
As the point slips into the coupler it will push the knuckle past the hook of the opposing knuckle. To assist the uncoupling you can push the knuckle tip outward with the point, when the knuckle tips are past each other you can now separate the uncoupled cars.