Lee is right, IMO. If you haven't enough exposure in the shadows to record the detail there, tweaking the development is not going to help much.

Soaking in the used pyrocat to increase overall stain is probably not going to work well - and why would you want to? What you need is shadow detail - not overall stain.

You might try semi-stand development for 16 to 20 minutes at 70F with a 2:2:100 dilution of Pyrocat (I do this with Kodak TMY 400). That should raise your maximum densities a bit.