Drive the Ghost into the portal so its wing makes contact with the portal's frame if you were to move towards it. The Ghost's wing needs to be inside the portal, with the rest of the Ghost outside of the portal. It works best on the left edge of the portal.
The Ghost's wing should be stuck inside the portal. Melee the Ghost until the wing is in the ground, it doesn't matter where you melee it.
Get inside of the Ghost
You can drive it off of the base by going down one of the ramps.