glCopyTexSubImage3DEXT alternatives

Hi all,

I’m currently implementing a GeForce7 fall-back path for a GeForce8 implementation that renders to a 3D-texture slice using FBOs.
Browsing through the available extensions on the GF7 it seems that there are no alternatives of doing glCopyTexSubImage3D for each slice.

Are there any fast-blit/copy paths/PBO+FBO constructs that may be faster ? If anyone already implemented this it would be great to get any feedback.