Backing off won't help either. If you keep the film CoC the same it will appear to add DoF, but if you (much more reasonably) use final print CoC the change in magnification will cancel this out.
Basically, assuming that you're constrained to a given CoC and s given diffraction-limited resolution at a constant final print size, there's nothing you can do. Not smaller format (which is what "backing off" really is), not different lens length, nothing.
The only possible improvement is stacked images in Photoshop. Or, of course, print smaller.