Chapter 4
by 
Ikr
What's next?
Make Vernon Cheat on Petunia
Of course Vernon could cheat on Petunia.
Though you assume this will need some work.
Maybe you could use some polyjuice potion to turn into Fleur Delacour to do this or into any friends you have like Hermione, Ginny, Luna, etc.?
(Comment for more options)