"locked themselves in a room with only the materials known to be on the mission and not only came up with the solution, but instructed some nervous, heat-stroked astronauts to build it."
not really, SkyLab was uninhabited until they got the fix up there.
The finished parasol, built from telescoping aluminum tubes and silver-and-orange fabric of nylon, Mylar and aluminum, was stowed aboard the crew’s Apollo spacecraft. At 9 a.m. on May 25, the crew — Commander Conrad, Joseph P. Kerwin and Paul J. Weitz — took off from the John F. Kennedy Space Center in Florida.
but you're still right
the CO2 scrubber solution for Apollo 13 was built in pretty much the way you described.
Using only the type of equipment and tools the crew had on board –including plastic Moon rock bags, cardboard, suit hoses, and duct tape — Smylie and his team conceived a configuration that just might work.