This is a lightweight alternative for Goldberg for the single purpose of unlocking DLCs. Just rename the game's steam_api.dll to steam_api.orig.dll, download steam_api.dll from releases and put it in place of the original steam_api.dll, the game will keep interacting with Steam as usual but it will consider all DLCs installed. Of course, you also need to download the actual DLC files from somewhere.

I've actually only tested it on Linux, so I'm curious to know if it works fine on Windows and MacOS.