Why all the fancy ideas about how to carry a pistol? It is not rocket science.
How do you usually carry it? If that interfers with carrying while backpacking then here are some solutions that work for me.
1) Hip carry @ 3 o'clock. There is no law that says you have to use the hip belt on your pack. Just buckle it to itself around the back of the pack. Wear a cover shirt just like you would if going to the store or a movie.
2) Chest holster. I use a kydex chest holster made by
http://www.survivalsheath.com/main/home.htm They are awesome holsters. It will fit either butt up or butt down depending on which one you get. Can be drawn downward from under your shirt or from the top through the neck line/open buttons. There are also other manufacturers. I just put that one out there because I have experience with it and my Air Marshal friend turned me on to them.
3) Shoulder holster. These will work but I have found that they seem to get in the way of the shoulder straps of the pack. Like I said it works but it was annoying to me. Maybe try a shoulder holster that adjusts for height so that you can wear it lower to the waist and not so high up in the armpit area. That may afford you more adjustability to get around the pack strap problem. Of course just wear a cover sirt with this.
4) Waist pack/fanny pack. Yes, yes, I know. You will look like a nerd, or a tourist, blah blah blah. Lucky for me I live in Florida and can wear one all the time. As long as I dress, say, in my work out clothes for short runs around town I just look like someone without any pockets hence the need for a waist pack. With hiking I don't think anyone would question one. Many people carry one in the woods as a convenient pouch for survival items and such. The waist pack puts the pistol in easy reach, is self concealed thus no need for cover shirts, keeps the pistol on your body, allows for free use of your packs hip belt.
My personal choice is either the chest rig or the waist pack. They both share most of the common merits that make them convenient and if I had to choose between those two it would probably be the waist pack.