You mean rgba8, depth and stencil?
First make sure stencil does work with FBO. I remember someone posted that it didn’t in early implementations.
Stencil can not be accessed with glCopyTexImage.
You could use glReadPixels with GL_STENCIL_INDEX and glTexImage2D to GL_ALPHA instead.
I think stencil renderbuffers are not possible on todays hardware. But I heard the ARB is working on an extension to provide a packed depth-stencil buffer format…