I know i'm not a mum yet, but i've done a lot of looking after small babies, one 5 evenings a week whilst the parents worked and the other was from age 2 weeks to 8 weeks when her mum was suffering from severe postnatal depression. The parents of the first used to make him sleep at certain times, which meant i pretty much had to coax him to sleep even if he wasn't tired, they told me to pat his bum or back slowly at a constant pace, but quite hard, obviously not hard enough to hurt. Its supposed to remind them of a heartbeat and is good for settling. To start with, took me well over 2 hours to get him to sleep, but eventually i had it down to no more than 10mins.
The other baby used to get really stressed and the bum patting didn't always work, but holding her against my chest, standing up with her and then swinging my body from side to side forcefully but steadily worked really well, especially if i sang to her at the same time. I had to have my hands and arms completely cradling her to me so that she didn't flail around and was secure.
Don't know whether you've tried these, but they could be worth a try if you haven't
