Running a Player vs Player Scenario

There's no way to do it with the normal dice roller, no. You could use the "/gmroll" feature (only you and the player rolling the dice see the result). You could also create a Character (for example: "Group1") and assign all the players in the first group to control it. Then you can use inline rolls in whispers, e.g. "/w Group1 [[1d20+5]]". You and all the players in group 1 would see the results. I would do it that way if you want everyone in the group to see the result for some reason.

You'll want to duplicate the campaign from the Campaign Details page and clicking on "Copy/Extend Campaign" option. If you're a Mentor, there's a tool they have access too called the Transmogrifier which allows a GM to copy pages, journals, cards etc from one campaign and paste them in another.