So, the solution fell into my lap anyways as a coworker is going out of town that weekend so I'll be working that entire weekend.
I told my mom (without letting on that I know about her shindig) about working that entire weekend. I told her how this is the best opportunity to make some serious money so that we can buy curtains for our place instead of leaving the stained blinds up and how I was looking forward to it. My mom kind of stared out into space and was chewing her lip alot.
Later on, my FI was talking to my mom and apparently she wanted him to tell me that his aunt was coming into town that day and wanted to meet me, etc etc. Well fine and dandy but FI ended up telling me what my mom told him to say rather than "my aunt's coming into town that day" lol. But I know what his aunt is like, she wouldn't be dropping everything to come to my city for one day (since she lives on the east side of Arizona). So I told my FI that I'll be seeing her at the wedding!
So I managed to get around it without screamin, shouting or threats.
Go me.