Is the idea that the user will sit in a chair in front of a real life table, and then the Virtual table should be in relatively the same place? If so, rather than relying on the Rift setup and player being in the centre of play space, you could have the user press/hold a button when they are sat on the chair in the real world.
When the button is pressed, call an event to set the position of the Pawn/Character in the world to also be in front of a table. That way, no matter what the setup, the player will always be able to use that button to put themselves in front of a table.
The PSVR uses this system if you hold the start button for two seconds, you need to recentre the user in your world.