How create Realy fixed joint

Hello, We are making a game, where some construction is built from different blocks. These blocks are bonded to each other with boards/staples. The hardness of these boards/staples in the attachment point is ultimate: that means if you fix one object in the space so that gravity couldn’t affect it, place the second object close to the first and bond this two objects with this board in some cases this board can be broken in the point where it is attached to one of the objects (because gravity affects the second object and it has weight). The second object in this case should fall under gravity. Integrated Unity physics doesn’t allow to make stiff joints between objects, objects act as though they were joined with some spring (even if we use FixedJoint). http://www.youtube.com/watch?v=AjbbPN1qQu4&feature=youtu.be

Does anybody know how to solve this problem? Maybe there are some settings for Joints, or some custom solution can be used. As a custom solution I mean some technique which will allow to make really stiff joints between objects (http://www.youtube.com/watch?v=Bf0M1sJG_BY&feature=youtu.be) and somehow calculate a force which affects the objects so that we could break joints if needed.