I've struggled with this as well and tried multiple things including modifying a Blackhawk holder on my camelback but there was almost no way to make that comfortable, plus the weight while running wasn't evenly distributed and it became awkward feeling......plus, concealment was almost impossible.
That being said, however, I'm glad I had it on me (it wasnt concealed) once on a run in E. Texas on a county road. I was running with a female and Cletus drove by slowly a couple of times in a car that just looked like something out of central casting for a serial killer
I finally turned to him and yelled, "WHAT?". My weapon was on the front of my rig and he sped off....so there is that.....
Lately however, I have taken to carrying a Glock 43 in a neoprene type band, brand name is Amphipod. Its smaller than a fanny pack and if I have it under my shirt, you'd have to be paying attention to know its there. If you are in BCS, go to Brazos Running Company and tell Mike what you are trying to do. He gets it and wont freak out if you want to see if your weapon fits. My review so far though is that it doesnt keep sweat off of the gun like I want it to, so I'm going to keep looking. However, in a pinch, it will do.