Can I assign 2 direct numbers to one phone and/or app?

Yeah there is a way, if I am understanding you correctly.

Solution:
Create another call queue. Add the user to the call queue. Assign that "special" number to the call queue. There is no need for the call queue to be a part of a Multi-level IVR.
Multi-level IVR = key presses for the callers.

It works with a call queue because if you go to
Phone System > Groups > Call queues > click on the call queue > Call Handling > Display Settings

here you can choose 2 caller ID's. I suggest you try using
1. Phone Number (this will display the dialed number, aka the "special" number)
2. Caller ID Name (this will display the number of the caller)

It doesn't work with assigning the number directly to a user, because if you go to
Users > click on a user > Call Handling > Settings > incoming caller Information
here you can only choose 1, either the dialed number, or the number of the caller.
Only call queues have the capability to display more information.