Whole Wheat Breads Dough Conditioner
Of the various things listed when looking up "dough conditioners" the only ones I'd think of using at home would be malted barley flour, lethicin and L-ascorbic acid (vitamin C.) An alternative for what the C is doing (oxidising) would be to buy your flour ahead and age it a few weeks for natural oxidising; possibly keeping it under refrigeration to reduce randicity, which can be an issue for whole wheat stored at room temperature or warmer.

That said, do I wonder if you are perhaps under-hydrating - whole wheat doughs tend to be obnoxiously sticky when "properly" hydrated - adding more flour to make them easy to work with is a common enough approach (been there, done that), with a common enough result that the end products are rock-hard... 

My personal preference at this point is to have a more easily worked dough that is not 100% whole wheat. You can view "non-whole wheat flour" as a "dough conditioner" of sorts in that light, if you like.