Thankfully the first option worked for me.
I feel it's worth noting that while adding another OS with YUMI under WINE seems to work fine, I've always had trouble setting up a fresh flash drive with YUMI under WINE, but maybe it's just me. Also, on one of my computers (Kubuntu 64-bit 3.8.0-31-generic) sometimes I would navigate around and the WINE file manager thing wouldn't see any files or hidden folders. If this hapens to you, paste the exact name of what it is you want to select (like "gparted-live-0.14.1-6-i486.iso" or ".hiddenfolder" and hit enter.