I can get source highlighting to work with
lesspipe or GNU
source-highlight, but both depend on environment variables that are specific to
less. How would I get syntax highlighting in most?
It doesn't do that:
most has no option for passing-through escape sequences which it partially-interprets. It will either treat the input as a binary file (which you wouldn't want), or as a text file. For the latter, it recognizes overstruck text (using backspaces), and can render those with a particular color. But that falls short of what's generally meant by syntax highlighting.