I don’t know if you have tried slugs in your Leshiy 2 magazine or even have a Leshiy 2. Your assumptions are just that. Most standard sized for caliber slugs drop straight thru the magazine which has not been a problem for me as I do not remove my magazine from the gun, instead I use a speed loader or just load them by hand. You can get some slugs sized a thousand or two over which may fit in the magazine tight enough to not drop out the front . I have tried both and do not see any appreciable difference in accuracy. The pellet or slug enters a tapered lead in the barrel which centers the slug / pellet as it engages the rifling . As far as the indexing goes, your statement that you would be lucky if the magazines hole would line up is a ridiculous statement. The gun is designed to properly index the holes inline with the barrel. It doesn’t make any difference shooting slugs or pellets as far as indexing goes.
Another thing you can do, is if your pellet (or slug) has a thin skirt, is you put the pellet skirt-down on a table and give the top of the pellet a light whack with a hammer. That's usually just enough to deform the skirt out a little bit, so it will fit snugly in the magazine. Adjust your whack strength (or number of whacks) appropriately for the pellet type.