Perhaps it’s time to consider bundling a tool with the CPython installer that does support this kind of package/environment manager workflow?
This would impose a lot of constraints on such a tool, and perhaps no existing tool wants or is capable of meeting these constraints. But if the PyPA made it clear they were interested and outlined the core requirements and constraints such a tool would need to meet, it would provide the opportunity for developers of such tools to assess the feasibility and express interest.