I saw a shoe repair guy use one of these years ago and had always figured it was some antique tool that had belonged to his grandfather or something... Nope!  It's real, and it's available, and if you have a bunion, or a pinkie toe that sticks out a little (like me) and makes one of your feet almost impossible to fit, especially in heavy work boots, then don't wait.  Bite the bullet and buy this thing.  I have tried every method possible for quite a few years, and nothing has worked until now.  I have 4 pairs of work boots that I've acquired over the past 7 or so years, all of them worn just enough to make them unreturnable, and just enough for me to realize that I couldn't "just wear them until they break in".  Now, since I got this device, I basically have 4 new pairs of boots for the price of the tool.

This isn't going to help you if you simply have the wrong size shoe.  But if it's a particular spot on your foot, and especially if you have an established history of that spot being hard to fit over several years, then this just might be the answer to your problem.  Clamp it on with the ball end on the interior of the shoe/boot, and use the screw knob to clamp it tight.  Tighter than you think, probably.  Leave it on overnight, then open it up, move it over slightly, and repeat.  Do this as many times as needed to make room for that prominent 5th metatarsal or the odd toe etc.  You'll feel the bulge in the shoe when you remove the clamp, and that bulge means more room inside your shoe, right where you need it.

If you're worried about scuffing the outside of the shoe, you could put a soft cloth between the tool and the leather while it's clamped.