I cut the etrogim on my cutting board and then dropped them - piece by piece - into the empty bottle. I tried to avoid the white parts but it wasn't that easy. Hopefully, it won't turn the vodka too bitter.
Because of Kedushat Shviit (etrogim are especially holy since they were grown during a shmita year and therefore, nothing can be thrown out.) I put all the fruit, the top and bottoms of the etrogim and any scraps that didn't go into the whiskey bottle, into a bag. I'm going to leave the bag on the windowsill until is rots enough to be thrown away. Hopefully it will rot quickly, I'd prefer not having them hang out too long in the kitchen!