I would suggest feeding a whole chicken wing a couple of times a week. Plunge the chicken wing into boiling water beforehand to kill any bacteria on the outside, but no need to cook. Especially to NOT bake.
While pumpkin and fibre may make the faeces firm. A bony meal will make it firmer.
Another alternative is to learn how to express the anal glands yourself and do this a few times a week.
Hope this helps.