Liddell was promoted from his role as first-team coach after boss Ronnie Moore left the club by mutual consent following a run of five games without a win.
With fellow coaches Paul Warne and Andy Dibble stepping up to assist Liddell until the end of the season, Liddell has moved swiftly to recruit Eaden to work with his defence.
"I played with Nicky at Barnsley and Wigan so I know him really well." Liddell told the club's official website.
"He has played in every tier of English football and played for some big clubs, and was assistant to Gary Johnson at Peterborough, so he will bring knowledge and experience.
"Myself and Paul Warne are obviously very attack-minded, whereas Nicky will be more suited to working with the defence. He is excited about the challenge and raring to go and we are really looking forward to working with him."