How do you make pie with Citron watermelon (not just the rind)?
...NadjaCS seems to have already answered this question above, but here's a link to a website which explicitly gives a recipe for a pie-melon pie using diced and flavored pie melon. It also has a link to an antique recipe for what appears to be candied pie melon slices; I'm sure you could use those slices in place of the base for some other fruit pie.

https://ganga108.wordpress.com/2013/08/30/pie/