Soaked some decomposing oak leaves for 36 hours in preboiled water with some yeast flakes. Stirred, put 1-2 ml into test tubes with 5 ml of malt beer ("Karamalz", I just picked a random brand), filled up with equal amounts of 5 % vinegar and whisky (didn’t have any vodka at hand). Put a thin layer of neutral vegetable oil on top.
Should keep out the vast majority of bad microbes and provide a mostly oxygen free environment for yeast.
IIRC, I’ve also read on suigeneris brewing that oak leaf litter has a 50 - 80 % chance of catching bretanomyce, which I’d be thrilled to find.
Yes it can be split somehow, but if you have to do lot of samples it can get quite long even at home.
I stored few strains of yeasts in fridge and when I had to reinoculate them on fresh plates to keep them alive for bit longer, I had work for few hours bit time sensitively split across 2 weeks.