So, according to the above rules interpretations. This should be legal.
DP hits a single, arrives at first safely. Flex is inserted to run for DP. Flex is starting pitcher or has pitched in the previous half-inning. Flex advances to second safely, therefore earned the base. Courtesy runner inserted for Flex(Pitcher).
Yes?
No.
"Earning your way on base" isn't the same thing as "earning a base".
Besides that, the courtesy runner rule specifically says that you can't do this.