Find an old site of yours that gets crawled regularly. Create a subdomain. Mirror the main page of your site on the subdomain. Wait for it to get crawled and indexed. Then put a 301 redirect to your real domain. This will make Google realize that your site which is relatively new is actually an old site that got moved to it’s own domain. Out of the sandbox you go!
or create a 3 page website. link page 1 to page 2, page 2 to page 3 and then page 3 to page 1. Vicious circle, eh
Dude, No black hat technique or anything which challenges the TOI's has not been used so there are no chances of getting banned if u use this technique. I agree you dont get banned for using 301 redirect.
i think there is only one to get out a domain from sandbox. adding content and wait. this is the way of getting out from sandbox