Excel 2007 : Help to custom format number with text

I've got several spreadsheets that I must re-do quarterly. The last column is a sum of hours and minutes from several other spreadsheets. That's another issue entirely. Right now the individual types in 8hr15m. Can someone help me with a custom format so that when she types it in, the text hr (space) m is already there? I'd like her to be able to just type in the numbers on a keypad. Thanks