Hi Leo –
There isn’t a direct way, but you can easily create a mask from the label file. There is a tool in the Delineation Toolbox called “Label Mask Tool” (it’s at the bottom of the toolbox). If you first press “Update List” and then select your structure, you can press “Make Mask” to generate a mask volume for just that object (this will overwrite whatever is currently in the mask buffer). If you then save this mask out, you could load it in as a label. It would be set to 255 for your structure, and 0 for everywhere else.
Will that give you what you need?