I would like to map 'shift-esc' to 'esc esc esc' on my macbook pro, but haven't find a way to do it.
I have tried Better Touch Tool, it can remap a key combination to another, but not to a sequence of keystrokes.
Within what application do you want this binding? I'm guessing Terminal or iTerm.
For iTerm, you can select Preferences > Keys then add a global shortcut to the action you want.
For Terminal it's similar. Preferences > Keyboard but you'll have to know the keystroke sequence in hex (I believe ESC is 0x35)
The other way to set shortcuts is in System Preferences > Keyboard > App Shortcuts. This is the easy way to map a menu option but may not be appropriate for your use case.