Dont think it is possible but you could use triggers to make the area under then unpathable.
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Considered easy altering of the unit textures?
http://static.sc2mapster.com/content/attachments/15/252/Screenshot2011-04-17_09_16_21.jpg
For my public assets look here!
http://www.sc2mapster.com/forums/resources/data-assets/46733-the-assets-of-evil/#1
TwoDie AuthorHow to place doodad using triggers that they would Use Footprints. Cause now units pass through and buildings can be built on. When placing same doodads in terrain editor they use the footprint.