How to output 3d geometries via grass plugins v.drape, v.to.3d in qgis?

When I try to process either a 2d Linestring or a 3d MultilinestringZ vector through the v.drape or v.to.3d processing tools in qgis, I get an error stating that it is outputting a 2d geometry instead of 3d and should set a lco flag to force 3d geometry:

WARNING: Vector map <output660b8ef0560648d183efaf4701ffc6ea> is 3D. Use format specific layer creation options (parameter 'lco') to export <in 3D rather than 2D (default).

This checks out because the file (that is created successfully) reports Geometry: Line(Linestring) in the layer properties

So, what flag is needed to force a 3d geometry with v.drape? I looked at the v.drape docs but could not determine what the lco flag should be.