Basicly as Yuri-BR said:
Merge the two depot together, comply projects, and copy the newly created csgo.exe from your relase, and binaries you'r are using; and start with some Steam emulator...(Dunno if real steam would work but i do not recommend it... use revemu or something like cream api, OR use goldberg, but on that there is no inventory emulator...)
update:
Proof of working (I use Goldberg with overlay)
However matchmaking/lobby is not working for me, it says that those files are unsigned... but i guess it is from goldberg, since it needs to replace steam dlls... So it makes sense
You can use console, but the stuff is working, it needs a lot of work, but it is working.