Hey Zac,
Ferrets can be stubborn on "where" they have chosen to be their designated pooping area. There are a few things you can do to help...As in a cage design, ferrets don't poop were they eat or sleep. So if Loki is pooping somewhere you don't want him to, change it to either an eating area or a sleeping area by adding blankets. You can also move your furniture around to help with this. However, sometimes, in the end, once they've decided that "that's the spot", you can't always fight them, you may just have to add a litter box there.
You can help by also doing POSITIVE reinforcement training. Instead of using a treat when Loki uses the litter box outside of the cage, use Ferretone. Vocalization work helps as well. Repeating the word "litter box" and praising your ferret for having used it outside of the cage. Keep in mind that ferrets are RARELY 100% with the litter box outside the cage, unlike cats. And they also have a tendency to go at doorways or heavily walked areas, as a way of marking their territory.
Hope some of this helps. In the end, if you can't beat em' join em'

(That wasn't we implying that you start pooping on the floor too, yuck!)
Good luck!
Jen