Oh, I completely understand that feeling. I kept my fish food under lock and key until DD was old enough to know that it contained shellfish, and the entire reason we went to ME feeding is that DH sort of 'sprinkled' fish food into the tank from about 14" above the hood, which meant that the front of the tank often was littered with allergenic fishy food residue... Yeah. I was NOT happy to be cleaning that up.
If you have a really great local aquarist shop, you could ask there if there's any long-term harm in feeding cichlid food to your guppies. I'm guessing that they may lose some of the flashy color over time, and might not reproduce, but that may be fine.