My MIL had told me after reading this blog post that she used to use a solution of vinegar and water to make permanent creases on pantlegs, but couldn’t remember the exact ratio. Well, if she reads this, she is welcome to comment/correct me on it, but I think I found it.
From the ThriftyFun website:
Simply mix 1/3rd of a cup of vinegar to 2/3rds of a cup of water. Using a spray bottle dampen the fabric in the area that you require the permanent crease. Cover with some brown paper or similar and iron.