Just posting this here for posterity because I couldn't find any information despite much Googling.

I had a few tablespoons of extra kefir grains and didn't have time to find someone to take them. I put them in a corner of my bin so that the worms could avoid them if they didn't like them. Today, that part of the bin is very popular. The worms appear to love the grains, and about half of what I put down has disappeared since last night.

I will update if I see any sick or dead worms in the next few days, but so far, everyone seems very lively and happy.

I did rinse the grains in water before putting them down, not so much for the sake of the worms but because I was concerned about possible odors if I left lots of kefir clinging to the grains. The grains so far haven't made the bin stinky or anything, but it's only been 12 hours. I'll update if I experience any odor problems as well.