Yeah, I had this same problem with the lift in DmRiot. The solution, given by Creavion, is to move the origin of the brush (not the pivot) in the MeshBrowser => Edit => Properties. Change the "Origin" coordinates (they reset to 0 as soon as they are applied, this is normal behaviour, don't worry). If the origin is in the floor for example, move the origin down so that the mesh goes down towers its origin. This is immediately applied to all instances of this mesh everywhere, so be careful.

In my case the origin was in the floor, about 48 units down, so I entered -48 in the Z coordinate of the Origin, and the mesh was lowered by this amount. Afterwards, all that is needed is to get it back in the appropriate location and it will drag its origin with it. The best way to use this is to set the origin in the middle of the mesh.