How to make Banana juice
If you microwave bananas for a few minutes in a bowl covered with plastic wrap and then dump everything into fine mesh strainer to sit for about 15 minutes, you will get a bunch of juice out.  Freezing the bananas before microwaving them works even better.

This technique was used in a (really good) banana bread recipe from Cooks Illustrated several years ago.  Once the juice is extracted, it is reduced, allowing more real bananas in the bread without making it too wet.