Take a look at the mag release, and especially the edge where it contacts the tail on the mags. The part is a stamping, and usually has a sharp edge due to the manufacturing process. That edge has a habit of grabbing on to the tail on the mag, making it tough to release. If you take a jewelers file, and "break" that edge, I think youll find all the mags release a lot smoother, and you should easily be able to do it with your middle finger while your hand is on the grip. You dont want to get carried away here, just lightly break or round that edge, and remove anything sharp. Ive done/do this to all my AK's, and its always solved the problem. The problem with filing on the mags is, it tends to make the mags "gun specific", which can be a problem if you have more than one AK.
Another place that benefits from a little filing is the selector and a small spot on the receiver. If you hit the little "tit" on the back of the selector (the part that makes the "arc") and the spot on the receiver where it rests when in the "safe" position, it will make the selector a lot easier to operate, especially with one finger and your hand on the grip. You mainly want to break the sharp point, and favor a slight slope towards the bottom. Depending on your receiver, you may have to break a ledge or shelf, or just smooth up a bend or fold in the metal. This will allow the selector to slide smoothly out of safe without hang up.