Bull made more than 300 appearances for the Shots before leaving for Brentford, where he made just six appearances.
Waddock said: "I know Nikki from our time together at QPR and Aldershot. He's a very good keeper and I look forward to working with him."
In Waddock's first campaign as manager at the Recreation Ground, Bull's career took off.
He played a key role in the club's promotion to the Football League in 2008, was named player of the year by the Non League Paper.
His success saw him secure a move to League One side Brentford last summer.
But, after rejecting the offer of a new one-year deal at Griffin Park, Bull has opted to be reunited with Waddock and Martin Kuhl at Wycombe.
Source: BBC Sport
Source: BBC Sport