To Scott : as to soften, did you try mere water ?
Another thing : we talked of Vallejo/Andrea paints here and there; their paints are very good, but they also produce a two component putty; as to me, it is pure crap, just opposite of Milliput. By the way, there was once a shortage of Milliput in France in hobby shops
( someone in Brussels- European Commission- may have considered that hobby shops were to be considered as toy shops, that toy shops are for kids, and that kids could collapse after having swallowed a big chunk of well mixed Milliput, so...) but we could nevertheless find it in art supplies shops; just a path to explore...