The Collaborative International Dictionary of English v.0.48:

Persuadable \Per*suad"a*ble\, a.
   That may be persuaded. -- Per*suad"a*ble*ness, n. --
   Per*suad"a*bly, adv.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "persuadable":
   accessible, admissive, amenable, cullible, deceivable, deludable,
   dupable, easy, exploitable, foolable, green, gullible, hoaxable,
   hoodwinkable, humbugable, impressionable, influenceable, ingenuous,
   malleable, movable, naive, open, open-minded, persuasible,
   pervious, plastic, pliable, pliant, receptive, responsive,
   seduceable, simple, soft, suasible, suggestible, susceptible,
   swayable, unsophisticated, victimizable, weak