Merging multiple groups of cells simultaneously?

In my spreadsheet, I want to merge cells A1 and A2, B1 and B2, C1 and C2, etc. so that the whole top row of cells will be two rows tall, but still one column wide. Is there any way to do this without having to merge each two-cell group one at a time? Like, can I tell excel to merge the two rows for every column of the spreadsheet?

Or, if that can't be done, is there any shortcut to merge the cells or do I have to use the "Merge & Center" button?

Edit: To explain better, I want the top cell in each column to be two rows tall. The reason for this is that some columns require a single value, while others require two values, and to keep it looking neat I would like to merge the cells for single-value columns. And since there are far more single-value columns, it makes sense to merge the top two cells of every column then unmerge as needed.