Make seitan "fattier"
I have been experimenting with this very thing, which is how I stumbled on this conversation. Real meat (I'm not a vegetarian so I can easily compare) has a different mouth feel. Deli meat feels stretchy and fatty, which seitan never does. It's just stretchy. Adding oil to the mix just seems to make the seitan more brittle. My best luck so far is using the Chicago Diner (famous old vegetarian place) method which is to make the seitan straight, cook it, and THEN modify it. So they make and simmer their basic seitan, then slice and THEN marinade based on how they want it to come out. Different marinades for gyros, corned beef, or turkey. I'm having decent luck marinading my veggie ham (that's been cooked and sliced) in oil.