There's 2 options that I know would work.
You can run a TF2 dedicated server locally for yourself and install the necessary plugin to get it working (there's some guides around)
An easier way that works for me is to go on a surf server, record a demo, and every time you run TF2 and want to surf offline you can play that demo first and then load the map you want to play offline.
The command that you need to not fall of the ramp (sv_airaccelerate) is hidden and can't be used in TF2. Servers with plugins can access it. When you record a demo, it also records the sv convars, which includes sv_airaccelerate. So when you play that demo file, your game is configured with the appropriate sv_airaccelerate value.