Adrian,
Make a table with a single field, Number (Integer) data type, and fill this will numbers 1 to whatever the greatest number of labels you could ever imagine wanting printed at any instance.
Add this table to the query that the labels report is based on, no joins, and in the Criteria of this number field, enter:
<=[TheNameOfTheExistingLabelNumberIndicatorField]
You can add a control to the label design, bound to the number field in this counter table.