When they're really little, I like to use my hands as if they were the hen covering them up. One group was so distraught when I picked them up from the feed store that I finally opened the box (long drive), put my hand in, and covered them with it lightly. Instinct told them to go under that hand and they spent the whole drive cuddling and poking their heads through my fingers and put their backs against my hand - and no more peeps of distress. Those chicks were for a broody and that first day of handling made a big difference.
Another group from the mail- the hen decided she wasn't broody any more so I got to raise them. Same thing, lots of huddling under the hands (also used the MHP) - they always had food and water, but it was a big-to-do when the fresh food and fresh water showed up, like a birthday party every couple hours. Another hen adopted them when they were 11 days old (got really lucky) - and the whole time she had them they always mobbed me when I showed up. So the hands simulating the underside of the hen works - but you have to start young.