Luckily that's not an issue with that model, as it uses 16-bit chips instead of the standard 8-bit chips, so address line 15 isn't needed. However, what is an issue is that the 4 extra pins needed for TwinDie chips are NOT routed... Meaning your only chance would be to use actual 8Gbit chips and hope they work.
These are the chips you'd need. I really have no idea if Haswell U-series supports 8Gbit chips or not, but I may test with my machine at some point if you don't end up doing so beforehand. If you do decide to attempt this upgrade, let me know, and I can create the necessary SPD data for you.