Christine,
Matthew is correct, but you will need to aggregate corresponding to how your summary report now groups.
For example, if you had Tiering by Customer Purchases by month, then you would need to have a table with a key field like
Customer number - YYYMM
The issue is how to initialize that table and how to maintain it going forward.
The initial load can be be via a summary report.
The maintenance can be done via an Action to detect that the required Summary record does not yet exists. Then have a safety net report daily report Subscription to see if somehow any are missing.