The Collaborative International Dictionary of English v.0.48:

Performable \Per*form"a*ble\, a.
   Admitting of being performed, done, or executed; practicable.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "performable":
   achievable, actable, attainable, compassable, doable, feasible,
   manageable, maneuverable, manipulatable, negotiable, operable,
   operatable, overcomable, practicable, practical, realizable,
   superable, surmountable, viable, workable