Wish to use simple supervisor hierarchy with increased limits for certain people

This is for Requisition and Purchase Order Approvals only.  We are planning to move away from Position Hierarchy and use Supervisor hierarchy due to it's simple structure.

We have a simple job structure e.g. Manager, Director, each job with a fix approval limit. But there are certain People who have higher approval limits.

Like Manager 'A','C' and Director 'A','M'  has double approval limits. They are individual people linked to standard jobs.

How can we handle it in supervisor hierarchy OR supervisor hierarchy with AME.

Thanks in advance.

Regards

-  Gyan Sharma