Working on rewiring a dozen 1910 gas/electric sconces to remediate some old K&T wiring, I'm in IL - US. The fixtures are supported by the gas line, and have no box. Gasfitter confirmed all the lines are disconnected and not live.

Trying to piece together some strategy before I go cutting holes in the wall. Initial idea is to enlarge the ~1" hole in the plaster to fit a 4" pancake box and use the center hole to pass the gas line used for support. Then I could pull the old K&T wires in and cap them off and run new MC up the wall.

Not sure how code compliant having the unused gas line pass through the box for support is though?

On the K&T coming up from the basement can I just cut them there, pull the live ends out of the ceiling to a J box until the last of the circuit is dead then shove them back into the ceiling?