Robert its proven already, my grandmother had tree in Chicago for many years when i was small that uncles and cousins buried each season.
They dug trench, brought branches together after trimming it tied branches with twine and wrapped in burlap, dug around roots splitting many and knocked tree in trench. Put plywood on top then they would shovel dirt on top. Plywood wood protect tree from shovel when taking dirt out next season. The root part was covered with much dirt and the whole thing when done looked like a big big pile of dirt.
Yes they can be grown inground and protected for winter in Chicago.

Yes Martin, I have read your posting and others about burying fig trees in cold zones. 

Hi Bob,
  I see what your saying now like in those pictures i have seen.

Bob for me that would not be the way to go because being i enjoy going outside enjoying there beauty as an upright tree.

Bob you do not need a special weeping tree to grow like they do in Asia.
You can use any type fig tree simply by training it , for example.

By starting out with a new small fig plant inground one would just hook and stake the branches parallel to the ground and keep doing this as the branch keeps growing . By useing a few low growing branches at first it would be easy to do.

Martin I agree,any fig can be made to grow close to groun d with a little work.
This should be the way in very cold winters climate,and not trying to protect a tall tree while upright.