Could haunting guise magic pen not be a unique passive?

With the removal of the ability to buy multiple pairs of boots, my favorite Dr. Mundo build died with it: It wouldn't be something that would be brought into Ranked games, since it's completely based around your Q, but with that build, your Q would just deal insane amounts of damage. However, since I couldn't buy multiple boots, I decided to edit the build a bit, for a different build: But I didn't know that Haunting Guise magic penetration was a unique passive, so the build was obsolete since you couldn't reach the desired amount of Magic Penetration.

It's not like anybody would find a way to abuse this, 2 Haunting Guises is 3000 gold which would put you too behind in your full build compared to other people.

I just don't want my goofy Dr. Mundo build to die.

So please, make Haunting Guise magic penetration not a Unique Passive.