It took a few minutes of trial and error to work out how but here's how to do it.
To add an entry in the command palette to open a specific file, add a modified version of the following template to your user Default.sublime-commands file.
// Modify the caption "File Open: Whatever" to something // appropriate and of course change the file path. { "caption": "File Open: Whatever", "command": "open_file", "args": {"file": "/path/to/whatever"} },
To add a key binding to open a specific file, add a modified version of the following template to your user Default (OS).sublime-keymap file.
// Modify the key bindings to what you want and change the file path. { "keys": ["ctrl+t", "ctrl+w"], "command": "open_file", "args": {"file": "/path/to/whatever"} },
Hope this helps.