Well, I went ahead and wrote a short plugin to do this. In case anyone else needs to do something like this, it's straightforward to modify. It's just an extension of EventListener that gets called each time focus changes. This is my first foray into the ST API, so if anyone sees this and knows ways to make it simpler/cleaner, let me know!
import sublime, sublime_plugin
class PythonREPLHelperCommand(sublime_plugin.EventListener):
def on_activated(self, view):
syntax = view.settings().get('syntax')
if syntax=='Packages/Python/Python.tmLanguage':
plugin_settings = sublime.load_settings('SublimeREPL.sublime-settings')
plugin_settings.set("show_transferred_text", True)
else:
plugin_settings = sublime.load_settings('SublimeREPL.sublime-settings')
plugin_settings.set("show_transferred_text", False)
But I'd still love to know if it's possible to do this without a plugin!