Hi Richie,
The way I've done this in the past is to put everything you want to preview into a group, and name the group something like "Preview". Turn the visibility eyeball off. Then in the OnPreviewRender call, put something like:
Dim Preview as xpBaseObject
Self.GetObjectByName("Preview", Preview)
Preview.Visible = True
In an upcoming release we'll be able to do it with Visual Logic. There will be a be an "Is Online" block for the scene returning a True/False. Then you can set the visibility for that same preview group based on the value of "Is Online"
Hope that helps.
Chris
#XPression