The Collaborative International Dictionary of English v.0.48:

Pickapack \Pick"a*pack`\, adv.
   Pickaback.
   [1913 Webster] Pickax

The Collaborative International Dictionary of English v.0.48:

Pickaback \Pick"a*back`\ (p[i^]k"[.a]*b[a^]k`), adv.
   On the back or shoulders; as, to ride pickback. [Written also
   pickapack, pickback, and pickpack.]

   Syn: piggyback.
        [1913 Webster +PJC]

              A woman stooping to take a child pickaback.
                                                  --R,Jefferies.
        [1913 Webster]