Manual glitch: if you know how to do the manual glitch in shop using a cosmetic, then you can do that to the soft as well. Click a cosmetic in the shop (not inventory), and then go to your inventory and click on the cosmetic you wish to resize. Click on your avatar and open the resize tool for the shop cosmetic (will be at the very top), and it will allow you to resize the softed cosmetic rather than the shop item. When you save your outfit, the softed cosmetic will stay resized permanently.
This manual glitch is shown in this tutorial at the 7:15 mark.