finishing culled layer hens

I love the rich yellow fat that comes from a free range bird, regardless of age. What I have access to are 'retired' live birds from a nearby layer operation. I know that they are extremely affordable stewing birds, but won't have the same free-range taste or yellow fat. In terms of affordable meat, the thinking is to can the breasts, confit the thighs and legs, faux gras the livers, and make stock and broth from the carcasses (probably confit the gizzards as well - I LOVE gizzards; hearts go into Jacques Pepin chicken gizzard and heart soup recipe.) I might also grind a bit of chicken sausage meat if I get enough.

Since my parents live near the commercial layer operation and have a bit of pasture space (but don't want/not cost effective to grow out birds for me), I was thinking it might be more affordable to buy a dozen (or two) live culled layers, put out on pasture (and feed them screenings from the local grain elevator) for 2-3 weeks, and then harvest. How many weeks do you think it would take commercial layers to put a little color and flavor into their meat/carcass? Would 2-3 weeks be sufficient?

Anyone ever done this before?

Thanks!