Azure Stack Hub would be that answer to "how do I run Azure PaaS workloads on-prem", but :
- It's a very heavy solution, even in its evaluation version (ASDK). Probably way too complicated and costly for such an infrequent use, but that would be your decision to make ultimately.
- It's far from supporting every type of Azure PaaS workflow, so it may not even suit your needs.
So maybe you should start looking at a different solution, indeed...