Pan sauce without meat
I think de-glazing the cast iron pan would be a good solution.

After the meat is cooked, remove it from the cast iron pan, and with the pan still on the heat, add a small amount of liquid. Just about enough to cover the bottom of the pan 1/4 inch. Then scrape the bottom with wooden spoon to get up all that goodness stuck to the bottom.
Add this to your sauce to get the meat flavor into it.

Liquids you can use include: wine, stock, water, beer, probably a lot of other stuff. And the type of liquid to use would depend on the dish and personal preference.