Running validation multiple times on single request

[eluser]feel[/eluser]
Not quite. I only submit the form once, when I upload the excel spreadsheet. Then in my controller I parse the excel file. For each row I read from Excel file I do the same:
1. Set $_POST with values from the row
2. Run validation for ruleset "item/add"

In step 1. I don't unset $_POST but I update the values with the data read from current row.