you could stove top a gallon or so of dme and add in a package of lacto. hold at 100 or so for a 5 to 7 days or until it gets good and funky, pasteurizer, and then add back into the main batch. that's how i did mine and i didn't think my final product was sour enough, but with the combination of your primary acidulated batch and the secondary addition of some lacto-wort, you might come out just right.