Meaning: extremely easy
Rewrite 1: as easy as falling out of a tree
Rewrite 2: as simple as walking down a step
Rewrite 3: as effortless as flippingts2b a switch
(Gleaned from an unintended repeat of this cliché from 12.20.05:)
Rewrite 4: as easy as tripping2 down a step
Rewrite 5: as easy as stepping2a through a doorway
Rewrite 6: like taking a sip through a straw2
Rewrite 7: like wiping the crumbs off your face

Comment: I tried to recreate the exact sense of the simile, then twist it just enough to give it new meaning by looking at synonyms for “easy.” Some others to consider are trouble-free, straight-forward, uncomplicated, undemanding, and painless* (example: as undemanding as a sleeping baby).

*This list is from Microsoft Word's thesaurus. For a more thorough list, try Merriam-Webster's Thesaurus.