I don't have a option to bath unless it's a super nice hot day which doesn't happen around here often so I use Healthy Hair Care. You buy it as a concentrate and add water in a spray bottle, if you use it whenever you groom it works wonders!! Helps to add shine as well! Cuts my grooming time down by half as I don't spend twenty minutes removing dirt, dust and hair dander
Professional dog groomer, here. High Velocity Blow Dryer. Used it just today on my bison-coated two-year-old Gotland Pony. Requires some training much like acclimating to a water hose, but even my most fractious gelding learned to love it. We hardly brush out any winter coat on our boys, which all grow at least two inches.
My second-best tool is a good chamois (the Absorber is my favorite brand). Pulls anything loose out of a dry coat, pulled with the hair growth.
I hose my horses off after every ride when they are sweaty. A full body soaking....and I never have the dust problem in the summer when I hose them daily. I don't know if it is hot where you are, or if you ride hard enough to make a hosing necessary, though. Or maybe you have access to warm water? That would be good when he isn't sweaty enough to make it necessary.
So of you can't hose daily, try spraying apple cider vinegar on his whole body after grooming. Then, take a dry towel and wipe it all off. I do this in the winter when hosing isn't an option.