Use Blender 2.54, with OBJ Exporter patch from here: http://www.blendernation.com/2010/09/12/blender-2-54-beta-released/.

Create a mesh with quads, not triangles, and make sure they have a uv mapping. (see attached tree01.blend)

Export the mesh using OBJ exporter and select the triangulate option. These are the options I'm using:
True, # EXPORT_TRI
False, # EXPORT_EDGES
True, # EXPORT_NORMALS
False, # EXPORT_NORMALS_HQ, # not yet
True, # EXPORT_UV, # ok
True, # EXPORT_MTL,
False, # EXPORT_COPY_IMAGES,
True, # EXPORT_APPLY_MODIFIERS, # ok
True, # EXPORT_ROTX90, # wrong
True, # EXPORT_BLEN_OBS,
True, # EXPORT_GROUP_BY_OB,
False, # EXPORT_GROUP_BY_MAT,
False, # EXPORT_KEEP_VERT_ORDER,
False, # EXPORT_POLYGROUPS,
False, # EXPORT_CURVE_AS_NURBS,
False, # EXPORT_SEL_ONLY, # ok
False, # EXPORT_ALL_SCENES, # XXX not working atm
False); # EXPORT_ANIMATION): # Not used

The resultant OBJ has triangle faces, but each triangle that was sourced from the same quad ends up with the same texcoords. eg.

f 123/7/113 119/8/109 118/4/112
f 123/7/113 118/8/112 121/4/114
f 118/4/112 122/5/111 125/6/115
f 118/4/112 125/5/115 120/6/116
f 120/1/116 126/2/117 121/3/114
f 120/1/116 121/2/114 118/3/112

Notice the texcoord index (the middle coord) for each pair of faces is the same.