Excel color scale based on alphabetical order

I like Excel's color scale feature in the Conditional Formatting menu and I am trying to get it to work for text values.

The way it works for numerical values is that it color-codes the lowest and highest values each with a certain color and then any values in between form a gradient between the min and max colors.

I'd like to be able to do this with text based on the alphabetical order. So let's say I have a table of:

A A B C
B C D A

"A" would be the lowest value and "D" is the highest. I've applied the color scale to the table but none of the cells get colored. It seems like the values need to be numerical for a color scale to work. Is there a way to make this work? I'd rather not dive into any VB macros.

Using Excel 2010