WordNet (r) 3.0 (2006):

slap on
    v 1: apply carelessly; "slap some paint onto the wall" [syn:
         slap on, clap on, slam on]

Moby Thesaurus II by Grady Ward, 1.0:

50 Moby Thesaurus words for "slap on":
   add, adjoin, affix, agglutinate, annex, append, attach, bedaub,
   besmear, burden, butter, coat, complicate, conjoin, dab, daub,
   decorate, enamel, encumber, gild, gloss, glue on, hitch on, infix,
   join with, lacquer, lay on, ornament, paste on, plus, postfix,
   prefix, prime, put with, saddle with, slather, smear, smear on,
   spread on, spread with, subjoin, suffix, superadd, superpose,
   tack on, tag, tag on, tar, undercoat, unite with