Pretty much this, but Black Mask's legs are actually soft enough to morph them into shape just enough to get that right adjustment. While I had no problems keeping BM figure standing, every time I put him on the table and someone bumped it, he'd always fall over. Being the nit-picky person that I am, I got annoyed with that and so I went about heating up the legs and cooling it down and voila! The figure could literally keep standing on its own even when I'm purposely bumping the table he's standing on (the figure even jumped and landed squarely for a second when I pushed the table too hard just to try and make it fall).
Use the hair dryer and heat up the legs for at least 1-2 minutes. Afterwards, you can bend around the knee area and adjust the way his legs are bent. For mine, I bent the right knee and adjusted the plastic around the right ankle so it's straightened out a bit. I also bent the left knee by a small margin just to keep that uniformed look. All of this was done so the right leg doesn't always have to be pushed too far back just to make him stand (originally I had to always push his legs far back just to keep him upright, now he just looks normal the way he's standing).
Once you get the vague position you want, keep those positions nice and firm with your hands and hold them steady. Take them to the nearest tap/faucet and douse the whole figure under cold water. Another alternative to this is to have a big bowl/container with cold water right next to you and you can just dunk him in along with your hands (keeping the figure steady with your hands is essential because otherwise if you let go, the figure might bend back into its original shape). Just to be sure, I put mine in the freezer afterwards for literally 30 minutes to an hour just so it stays with the new position as it cools the figure, down to the last bit of internal plastic in there.
It's pretty easy to do, and in the case of Black Mask's legs (which are very easy to bend around once you've heated them up), it's actually a fun case of trial and error, and a simple matter of choosing what kind of leg stance you want him in. The photos in my review a few pages back already has his legs modified so that gives you an idea on how it looks pretty damn seamless. Not only does it improve the figure's stability, but it actually makes it much more fun to pose him around even with the limited articulation.
@Legion19
If you want I can take a photo of my modded figure from the side, to sort of give you an idea on how his legs were originally positioned in comparison to how it looks now.
