There is a work around to achieve this. Attaching a sample qvw for you.
Steps to reproduce my solution:
1. Create initial expression: Expr1
2. Turn off Values on data points & text as pop up for Expr1
3. In Presentation tab turn off Pop-up labels
4. Add new Expression Expr2, with your custom pop up definition:
='There are ' & Num(Expr1,'# ##0') & ' cards that generate a yearly cost of ' & Num(Expr1 * 12,'# ##0')
5. Make sure "Text as Pop-up is turned on.
custom pie chart pop up.qvw 199.2 K