...However it is soft leather and I have never tried this using soft leather. Has anyone molded their gun in a soft leather holster?...
I made a magazine holster from scrap leather from a local surplus store. It was very flexible leather which I'm sure is cowhide. I wet the leather, formed it over a block of waxed wood, clamped the sides of the leather and added a weight on top and then let it dry. I deliberately put the rough sides outward to better hold in place inside my rear pocket.
The holster went through a number of changes while I was making it, hence the reason for the no longer used stitching holes.
I heated the leather with a heat gun and melted beeswax into it to waterproof it.
I had condensation issues so I punched holes in the leather for better ventilation in my rear pocket.
FYI, the light colored areas where I had cut a bevel on the edges have now darkened up with use.
I do plan to remake this magazine holster from horsehide. But it has been working well as is. The magazine is offset to make it comfortable when sitting. All of the commercial magazine pocket holsters had the magazines centered, so I made my own offset holster.
As you got the holster cheap, what have you got to lose by experimenting on it? If it was mine and it wasn't working as I wanted it to I would try to modify it.
With shipping, I paid about $85 for a horsehide pocket holster for my P356X. It had some issues so I modified the stitching to make it work for me. Then to improve ventilation I also punched holes in it like my magazine holster.