For what it's worth, In the Marshmallow Test book, the author mentions that prior to the test, the experimenter spent 15 minutes interacting with the child to build trust. They gave the child a bell, and the researcher would explain that if the researcher left the room, the child could ding the bell to bring the researcher back. They'd do a few iterations of this, with the researcher promptly rushing back each time, in order to build trust.
Perhaps not a complete solution, but the problem was at least addressed.
Josh Waitzkin describes something like this in his book The Art of Learning. Basically, he broke his arm a few months before an important martial arts tournament. While it was immobilized in a sling, he worked out the other arm then meditated, imagining he was working out the busted arm. He reported that this helped keep his bad arm from atrophying and becoming weak while he couldn't use it.
“Poor Faulkner. Does he really think big emotions come from big words? He thinks I don’t know the ten-dollar words. I know them all right. But there are older and simpler and better words, and those are the ones I use.”