Hi Alain - I don’t know if there is an easier way, but it may help to run this plug-in that explodes all the parts of a block to separate layers - then export using layers as the organizer. . Note the command line option - my guess is that you want the non-default option but experiment…
ExplodeBlocksToLayers.rhp (14.5 KB)
Drag and drop onto Rhino and run the command ExplodeBlocksToLayers
-Pascal