Open the geometry in SpaceClaim and use two planes to slice the body at the center to create a vertex to use. On the Workbench tab, click the Share button to reconnect the four pieces in the Mesh. In Mechanical, when you select Vertex, there will be a vertex in the geometry for you to choose.
It is generally a bad idea to apply a displacement BC to a single node in a solid mesh because that creates a high stress since the reaction force has zero area. Instead of a vertex, you could project a small circle onto the outside face of the solid, then you would have a finite area that you could use to scope a Remote Displacement to.
If the geometry is a thin-walled container, you can use a midsurface operation in SpaceClaim to replace the solid container wall with a surface body. You can keep the solid ends and use Shared Topology to have the solid mesh connect with the shell elements on the container.