1. Say you already thought you were in one and that you have a second family.
2. Hire actors to play the second family. Make sure you're second wife is much hotter then your current.
3. Insist on making your current wife meet your second wife and family.
4. You second wife is into the open relation ship thing too, but she does not like your current wife.
5. Tell your current wife that she is a dumb frumpy whore and that you were getting sick of here any way and want to move onto wife number 3, so you want current wife to give you an annulment because an open marriage isn't a real marriage.
6. After the annulment, find a women who is not a retard.