Extension tubes for shallow depth of field?

Will using extension tubes at non-macro distances give a shallower depth of field than without them? I always hear people complaining that extension tubes give them super shallow depth of field, so for example, could I turn my 50mm f1.4 DOF into f1.2 DOF at portrait distances?

Can someone do a test?

Thanks!

Won't work. Extension tubes yield shallow DOF BECAUSE they allow the lens to focus closer than it's MFD. Even with focus set to infinity, with an extension tube attached, the lens will only focus on an object that is a few inches to a few feet away, depending upon the length of the extension tube.

Dang, just found a calculator, that's a drastic change in max focus distance!