Get a
registry editor.
Got to:
HKEY_CURRENT_USER\Software\Microsoft\Today\Keys\
and create 2 new keys:
112
113
Inside each key there is a (Default) value. Change that to what text you'd like on the button (112 is the left one. 113 the right).
Create the string value "Open" (no quotes) with the path to the executable or document in BOTH keys (112 and 113).