So for any mods you downloaded they are stored in the drive your game is installed on, the directory of these mods is [Steamdirectory]\steamapps\workshop\content\1420350 (that number is the workshop ID for the game, you can figure this out for any game by just looking at the URL for their store page). In that directory you will find more numbered directories each carrying the files for a mod you have downloaded/subscribed to.

Now for getting those mods to work you can just take the .fra file(s) for a mod from it's workshop directory and transfer said file(s) to the custom directory where the game is installed so [Steamdirectory]\steamapps\common\Fraymakers\custom (you may need to create the custom directory} therefore treating & loading it as a local mod.

That should do the job. (I just tested it and it does work so enjoy!)