I've taken to running through my forges and loading up all the ore, back through a second time with coal - this gives them enough time to go from 20/20 to 19/20, then back through a third time with one more coal each to get them back to 20/20. They take care of themselves from there.

It sounds like more of a hassle than it is when you type it out, but when I get back from wherever/whatever, everything will be smelted and all the coal will be used, ready for another round.

And of course, you can always just get the mod that fixes the ratio and skip all that.