If you want a chick to think you are its momma - you gotta act like her momma. LOTS of handling and holding. Bring her every where with you. Hand feed her yummy stuff. Reward her for following you around. Lots and lots of time with her.
My daughter imprinted on one of her chicks - kind of by accident. It was her/our favorite little chick, so she did everything with her. She would watch TV with the little thing sleeping her chest, kind of under her chin. She'd sit for hours with her on her lap watching chicken-TV in the basement by the brooder.
Now, as a bantam-big-girl, she comes in the house every morning and wakes my daughter up. Bwack-bwack-bwack-wake-up-momma-bwack-bwack-bwack. They get ready for school together and eat breakfast together. And, just about every supper, also. I have tons of pictures of them watching TV together, too.