I know it might not be possible but this is what I do:
I use the cups they came in (I know yours will be in bags) and they float in the big tank to keep warm, I acclimate them to the tank water so that each day I can take my extra cup, scoop up new tank water and I actually pour out gently their cups into a bucket bellow me, catch them in my hand and swiftly put them into the new cup. You can also you a net if you think you can do that, if they don't have huge fins it should be alright for them.
But another thing, instead of using mason jars you can use Wal-Mart plastic cups, they have a round pack of 3 for a dollar something, super easy with screw on tops. You can poke holes in it for air exchange as well.
Just another idea is all ^_^ I know you plan on breeding so it might be pointless and better to practice jar care on the girls for when you do have fry