Every doc I can find discusses editing applicationHost.config in notepad to enable this.
The real need:
a) Via appcmd.exe or cmd line tool, enable dynamic compression to be configured in web.config (e.g. to set applicationHost.config -> "httpCompression" -> overrideModeDefault= to "Allow"
b) If 'a' cannot be done, then how, via appcmd.exe or cmd line tool, to enable site wide gzip dynamic content compression for mime type application/x-javascript
I just spent half an hour exploring appcmd.exe, and searching the net, and have seen no examples of using appcmd.exe to flip the overrideModeDefault values