Incremental numbers on text

I am designing invoices and receipt books in InDesign CS5 where there have to be incremental numbers which appear on each invoice or receipt. In the case of the receipt book there are usually five receipts per page, each with its own number. 

I am currently using a link to an Excel document with the numbers.

The problem is that it means going to each page and linking the Excel document to the correct cell. There are between 50 and 100 pages so this is rather time consuming.

Is there an easier way of doing this?