How are you planning to get the files to Premiere? You have to use something like RayLight or Serious Magic's DVCPRO-HD decoder. Both will convert the pN files into 23.976 files, so if you're using those utilities (and shot in 24pN mode) then you'd want to use a 720 setting with a frame rate of 23.976.
I'm using Raylight. I'm converting the 24p Native without any pulldown and importing it into Premiere which does show it to be 23.97. When I export the project it should stay 24p.
I guess the issue I had with making a custom setting of 23.97 is that there is a 24p conversion method button. I wasn't sure if that was doing something I didn't want it to do. I'm guessing that is only used if it is a 60i project, I hope.
Is 24p Native such an odd format that Adobe doesn't want to officially support it?