EXPERIENCED MAMA'S!

Okay...I agreed to watch my nephew for a few weeks until they find a daycare. 
He is 1 yr old. Has been home with mom pretty much ever since the beginning. Still sleeps on mom every night and doesn't even nap in his crib. 
I'm not condoning this behavior at all! But it sure is making it hard on me- he doesn't like being away from mama and it takes me HOURS to put him to sleep because he gets pissed that I'm not his mom! 
We've tried rocking with a bottle, singing, patting/rubbing back, playing with hair. He will fall asleep quickly if we go on a walk but then wakes up as soon as we get back to the house. 
He gets so exhausted that he just ends up screaming non-stop until he gets so tired he'll finally let me hold him & he passes out.
We have a great time when he's not tired!!
 
Do you ladies have any tips?