I made a holster sewn to a heavy duty elastic band for wearing gym shorts and such. It is an IWB set-up, and I carry my small Kahr PM40 in it. That pistol is light enough to sit firmly against my body and stay in place when running. It can be positioned at any angle and at any height, anywhere on your body. With a heavy, full size 1911 loaded with ammo, there's no way this type of system would work, unless you beefed it up. If you went to a smaller pistol, you'd be ok.
I still want to buy one of those daily planner looking binders that carries a pistol inside it.