mklink needs admin rights. I'd also have to call it for every single file at which point I could just copy those files instead of linking them.
mklink /d , and have the program look for that folder. I use mklink /d to link my user folders from my spinny disk to my user profile on my SSD.
However that does leave the problem of admin rights. I mean, you could prompt for it, and have the description of the ReShade mod state that it will need admin permissions.
Wait, can you link to a dll in a subfolder as long as the .exe is in the parent? if not this wouldn't work.