Select the cell with the numbers in it and the cell below it. Right click, choose Format|Cells, on the Alignment tab check Merge cells and click OK. Set the row height of the first cell to the maximum. Increase the row height of the cell below so that you can see all your data.
That's a workaround, but I think you should tell your boss that lists of numbers should be entered in single cells in Excel. It's a spreadsheet, not a word processor.