Hi, Mary Lee. It's do-able, but not automatically. I've accomplished this by:
1. Inserting an autoshape.
2. Superimposing on top of it a text box formatted with no line and no fill and center-aligned.
3. Typing text into the text box and manually adjusting the text to make it appear to fit within the boundaries of the autoshape.
4. Grouping the autoshape and text box together.