Normally if you want to advertise a non existent route in the Cisco world, you'd need to create a null route to make that happen. I stumbled across the following post though when I was trying to suss out how to do the same in PAN-OS. In my case I wanted to advertise a GlobalProtect IP pool prefix across an AWS VPN using BGP.
I'm forever needing docs for Palo Alto considering that is now my weapon of choice in the fight against bad actors. The problem is that it can sometimes take me an age to find some of those useful docs that I use frequently if I lose them so I'm putting them here.