Similar to what Vojo indicates...
1) Create a User-defined Cell, call it User.AntiScale, but set its value = ThePage!PageScale/ThePage!DrawingScale
2) Set the Character Size value = GUARD(12 pt*User.AntiScale*Width/4.75) Adjust the initial size, 12 pt, or the width factor, 4.75, to get the desired beginning size and the amount of variation with shape resizing.