It doesn't sound feasible to instance open-world content. There is a simple way to accomplish this however. Add a hardmode to Incursion which flags every non-NM inside as Apex, with comparable stats and CP gained for the mob's level. A reduction in agro range would be appropriate (probably required to be viable,) due to the increased difficulty also increasing the risk of death which would make it less attractive as a grinding spot, but there should be no other major adjustments necessary to make this viable.