Question about global skills + undo in shop

Is using the 'undo' in shop an advantage for champions with global skills?

3 scenarios I can think of is :

Say, Ashe has ult and gold around 1600. She can buy the rod for + AP which is beneficial for her ult then exchange for BFSword/Zeal and Boots.

Another is Kart, where he can cast his ult with the rod, then undo after, and go with chalice of harmony + boots.

Last is Soraka, which badly needs her ult, goes for CDR boots, casts ult, undo then go for mobility.

No, it's not advantageous for those champions.

As soon as you perform any action the undo button will grey out and you won't be able to undo your last purchase.

This even happens if you do an action passively (such as Teemo stealth or Homeguards).