"All we need is your name to show you a preview", or "You won't need to enter anything else unless you purchase". Emphasise that the name is all you need, I think that would solve the issue.
Unfortunately there isn't an obvious affordance for this sort of interaction (that I've yet come across) - it looks like an email signup, when in fact it's more like 'play a game'...an interesting challenge...
It would be interesting to see if a vague 'what's your name' approach, rather than a specific direction with a stated outcome, wins in a split-test.