Here is what I would do:
Step 1: completely finish the game in silence
Step 2: make a teaser trailer simply stating that “Lamarr will be returning.”
Step 3: set the internal release date for a week after E3
Step 4: at E3, make your whole appearance there to show off DOTA 2
Step 5: at the end of E3, casually announce Ep3 is coming out next week
Step 6: watch the ensuing chaos
Step 7: release it a day late
Step 8: success!!!
Whats your ideas?