You could use the technique that I use when loading from my horn and bag. I sit the butt of my rifle on the toe of my boot and hold the forestock and barrel with my left hand. I carry my bag on my right side where I can easily reach things in it when I am loading. Since you will be loading from a bench, the bag will make no difference but I just mention it so you can see that it is possible to load your rifle without having to have a stand. Using the toe of your boot is great for keeping the butt of your rifle out of the mud when moving from one place to another as when shooting in a woodswalk. An even better idea for loading at a bench that is on concrete is to get a piece of carpet that measures about 1 foot by 1 foot and use it to sit the butt of your rifle on. A piece that size is plenty for the butt of your rifle to sit on and it is a size that is easily carried with you when you go to the range. If you are shooting from a concrete bench, you can cover it with an old blanket to protect your rifle from scratches. If you can find an old army blanket, they are a good protective thickness. An old saddle blanket is excellent, too. If you need something to lean your rifle on to load it, you can take a piece of pine 2 X 6 and cut a V or U shaped notch in the end of it. Clamp it to the bench and you have your rifle rest. One bit of serious caution is NEVER load at the shooting bench because of the danger of an errant spark getting to your powder supply and turning it into a bomb. Keep your powder and other loading supplies at some place behind the firing line where a spark from either your rifle or someone else's rifle ruining your day with an explosion that can possibly kill you. That is why muzzleloading ranges have loading benches behind the firing line.