I believe the no-cd fix was something separate from the Mk2 update, but don't quote me on that.
I found the following from a Google search;
https://www.gamecopyworld.com/games/pc_ ... %20UpdatesRail Simulator Mk2 [MULTI] No-DVD/Fixed EXE is the first link under Game Fixes. There is a warning when you try to download that FireFox may block it because it detects malware/virus and to use IE for the download. I was not feeling lucky so I didn't give it a try, I'll leave it to you to decide if it's worth the risk.
Download the PRB from page 51 of the Powder River Basin thread.