Yes, you can easily take the mattress off the old style sleeper sofas ... I believe that is the type they currently have in the VWL.
We always set up the bed for the kids this way when using the sleeper sofas. We first started doing this back when the kids were very little .. but had outgrown the pac and play ... and I was worried about them falling out of the bed. It's become a tradition now, and it's very comfy to sleep on, too. More support and no bar ! We just put everything back together each morning ... not much trouble at all !
HTH ...