A "Kill Secured" Item or Mastery

Hi, I main support and one of my least favorite thing to do as a support is to take a kill that my adc needs. Sometimes they're losing a duel and I need to contribute as much as I can to ensure their survival, sometimes they crit unexpectedly and my next ability takes the kill, either way I feel bad that my adc doesn't get the gold. Some adc's are good about it and some turn into sea salt and vinegar flavored chips. So what if there was a mastery or item that is similar to Kalista's passive that lets you secure a kill instead of take one? Supports don't have a ton of itemization and I think that this would add some variety and a mechanic that no one would complain about (unless you're trolling, in which case don't take the item/mastery).