sneakingly

from WordNet (r) 3.0 (2006)

sneakingly
    adv 1: in a sneaky manner; "I always felt sneakingly that I
           wanted to be a concert pianist"

from The Collaborative International Dictionary of English v.0.48

Sneaking \Sneak"ing\, a.
   Marked by cowardly concealment; deficient in openness and
   courage; underhand; mean; crouching. -- {Sneak"ing*ly}, adv.
   -- {Sneak"ing*ness}, n.
   [1913 Webster]