(without having to execute it first on Machine C)

Someone some where has to create the definition of the environment...
The easiest to go about it is to execute it one.
You can add to your code the following line
task.execute_remotely(queue_name='default')This will cause you code to stop running and enqueue itself on a specific queue.
Quite useful if you want to make sure everything works, (like run a single step) then continue on another machine.
Notice that switching between cpu/gpu packages is taken care by the trains-agent, so you can run on cpu machine for testing, then enqueue the same code and the trains-agent on the GPU machine will install the correct version of the packages (TF or PyTroch)