It depends how much JS you want on your Big.
Besides JS-Training and 1on1-Training, you gain JS by training JR and IS.
Here a few Options:
JS is the main thing to you and you really need it on your big, but your DR sucks:
-> 1on1 Guards leads to nice DR und okey JS, when you go back on IS you´ll gain some ups by that.
DR is okey but your trainee is missing on JS?
-> JS helps you out here
You think that a little JS is enought? JR is completely overratet?
-> IS also trains JS and should help you out on this scenario.
JR ist the main thing to have on a Big!!!
-> not really worth the deal.....unless your Big has a great Startvalue. Not worth it. Sorry :(
Well, you can try it that way though: Train some OD. Get some JR-Training (gives maybe +1/+2 ups in JS, depending how long you are training) and try to get you JS higher, by training IS. I doubt, that this will be effectiv.
I hope, this helps. :)
Regards Bommy