(I know this is an old thread, but since I dropped by looking for the same information and found it elsewhere, so here goes.)

If you've installed Sublime from the zip, follow the instructions from
http://www.howtogeek.com/107965/how-to-add-any-application-shortcut-to-windows-explorers-context-menu/
Scroll down to 'chapter' by the name 'All file types'.

Taking the above page's guide as an example, you can add a shortcut key to the context menu item by adding the text you like to 'Open with Nodepad' -key's (Default) string.

Here's my setup as exported from regedit:

Windows Registry Editor Version 5.00


[HKEY_CLASSES_ROOT\*\shell\Open with Sublime Text 2]

@="Open with S&ublime Text 2"

[HKEY_CLASSES_ROOT\*\shell\Open with Sublime Text 2\command]

@="c:\\apps\\tools\\sublime_text.exe \"%1\""