IS as a secondary for wingmen JS training will take forever. I've trained 18 year old rockie on JS for 1 full season (as a wingmen) and never popped in JS.
Sometime back I used the Hungary NT forum training speed prediction...whatever and it said 24 weeks for my 19 year old to get a pop in IS if I train his JS as a wingman.
So maybe a player can get a pop in IS from JS training as a wingman, but will take a looooooooooong time.