It's easy...I cheated! What you're looking at is really a copy of a pie chart, and it's easier to do than to explain how it's done! LOL
1) Create your pie chart, but don't publish it yet.
2) Left-click for "save image as", or use the Windows Snipping Tool to download the image as a JPEG file to Pictures, Favorites, Downloads, whatever.
3) Use the ADD MEME button below to upload your new jpeg image as you would any other photo for a custom template.
4a) Add text and publish the image of a new pie chart.
4b) If the text is already there, look for any open white area on the image and print a white-on-white letter to blend in with the white background, and then publish.
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Any questions?