I would still trim and shape the hair on the top part of the ears if you want them to stand completely erect. I'd do that before taping. My Blazer is 3/4 Yorkie and 1/4 Shih-Tzu. His ears stand up except the tips- one ear bends down just a little and the other sort of twists a little. I love how his ears look!
But anyway, mixed or not I'd trim the hair first then worry about taping. They could be droopy right now due to teething so a little shave could perk them right back up.