filled it with the leftover pastry cream, put cut fruit on top, glazed with an easy glaze (apricot preserves, plus a little booze--you could even use coconut rum! (or you could use water)--cook until melted, strain, brush over fruit). Voila! Easy dessert. And yummy, to boot!
All this to say: even 3/4 cup of leftover pastry cream can come in handy for a delicious dessert at a later date. Your freezer and freezer bags (plus a Sharpie to mark the date) should be your best friends, if they aren't already.