WordNet sense 1 (supplement what is thought to be deficient):

eke out

WordNet sense 2 (line or stuff with soft material):

pad

WordNet sense 3 (make fat or plump):

fat, fatten, plump, plump out, fatten out, fatten up, flesh out

WordNet sense 4 (write all the required information onto a form):

complete, fill in, make out

WordNet sense 5 (make bigger or better or more complete):

round out

WordNet sense 6 (become round, plump, or shapely):

round