I have seen some creative ways to do a backpack mount for actioncameras, but none could I make from what I already had. So I came up with the idea of using my regular tripod as the base component. The main reason why I want to use my tripod is that I already have it in my backpack when I'm out.
The base idea is to stuck the tripod in the sidepocket of the backpack and strap 2 legs tight to the backpack and let the third point outward with the camera attached to it.

This is how I did it:

Step 1: The Tripod Leg Insert

I took a piece of plastic rod and started lathening it down to the desired diameter (14.2 for my tripod). I cut it to a 40mm piece and drilled a 6.8mm hole for the tapping to the M8 bolt on the camerahead.

Step 2: Glueing the Insert Into the Tripod Leg

Next step was to glue the insert in the tripod leg. Because the insert is made of a "fat" plastic, not every glue will work. I found that Loctite All Plastics would do the job.
The insert has a tight fit (I had to hammer it into place) and I dont think the glue was necessary at all, but I took it just in case. An other option would be to take a hammer and an awl to make a small hole in the tripod leg, into the insert.
Dont lose the rubbertip for the tripod leg, just put it back again when the insert is in place!

Step 3: Making the Camerahead Mountable on the Tripod Leg

For the head, I had a crappy traveltripod that I slaughtered. After I've removed the bottom plate, the legs fell off and I had a M3 hole left in the head where I put a small M3 rod. The other end is attached to a M3 hole i drilled and tapped in a regular M8 bolt.
All this, when attached is glued together with som standard epoxi so it doesn't loosen or brake easy.

Note: The M8 bolt can be seen at previous step with the M3 rod inserted

Step 4: Attach It to the Backpack

My backpack is kind of ideal for this way of attaching the tripod. It has sidepockets with straps over it and more straps higher up.
This is how I attached it and even though the tripod has more weight than other backpack mount solutions, I dont find it disturbing yet.

Tip: If you want to use your tripod as a pole mount for your camera its easy. Just unscrew a bolt at a joint connection on the tripod.