You can use the whey for lacto-fermenting many things. I haven't done this myself as I just found a source for raw milk, but this blog has many entries on the topic:
30 Second Lacto-fermented Salsa | CHEESESLAVE
Lacto-fermented Ketchup — and French Fries! | CHEESESLAVE
Homemade Lacto-Fermented Mayonnaise | CHEESESLAVE
Lacto-Fermented Dill Pickles | CHEESESLAVE
I think the book "Nourishing Traditions" also has some tips/recipes for whey.