i plan to change my 2 rings to a 3 up front. this is an old 10 speed and the fd has a built in cable stop and the derail cables make their turn above the bottom bracket. a short length of cable housing runs from the turn at the bb to the fd cable stop. there are no triple fd with a built in cable stop so i need to add one. the seat tube is 1 1/8, i am looking for a stop.
1 using a cable stop hanger from a front brake steering stem 1 1/8.
2 a seat post clamp with a rear brake cable hanger for 1 1/8.
3 i can make a stop using a cut down rifle/pistol cartridge case, using the primer hole as a stop, a saddle to match the tube and case radius and a hose clamp.
4 any ideas?

No need to to all that work. Run the housing from the lower downtube fulcrum (cable stop) under the BB and up between the chainstays ending it anywhere short of the new FD. Your bike will now function like a modern bike with a BB cable guide.

That's what most of did as we moved out of the Bronze Age and the replacement FDs for our old bikes no longer had cable stops.