My thought would be to allow us to specify a placed block as an "evolution stone".
{
"evolutionRock": "pixelmon:pc",
"maxRangeSquared": 30,
"evoConditionType": "evolutionRock"
}
The above is just a quick example I threw together but hopefully gets the point across on what I'm looking for/hoping for.
Adding the possibility for nbt data could also be even nicer in the future but I'm trying not to push my luck here..