By adding half the peaches in secondary. The peach flavour is subtle but it is definitely present. I also used a cider yeast, so it was nearly at its ABV limit when the peaches were added, maybe that helped slow down the fermentation as well.
https://meadmaking.wiki/en/home
In terms of advise, don’t bother simmering your honey as this will remove a lot of the flavour and buy some yeast nutrient if you want to drink it early. The nutrient will make your mead drinkable without having to age it for over a year, cause yeast needs nitrogen and unhappy yeast makes rocket fuel that needs to age out. When in doubt, age it out. Apart from that, just play around, use the GotMead calculator to estimate ABV and have fun.
Don’t you want a dominant gene? Anyway, if you want to know more watch: Unnatural Selection, Episode 3. It’s on Netflix and worth a watch, it discusses gene drive in detail.