Nothing fits the description better than eleocharis parvula. (dwarf hairgrass) ...It stays around 5 cm. If you can't get that, eleocharis acicularis (also called dwarf hairgrass) grows slightly taller...to a little over 10 cm but it also needs higher light. The leaves are really thin, like hair. E. Parvila should be OK at 2 WPG. It might go slightly lower. THIS GUY is growing it in a 45ish gallon with 2 39 watt bulbs.
http://www.plantedtank.net/forums/tank-journals-photo-album/83809-36x18x18-rimless-2.html
The person used probably jungle vals, onion plant, and some kind of tiny sword. Either microsword or pygmy chain sword. These plants have thicker leaves, more like cat-tails or crabgrass. IF you want a tall plant with hairlike leaves there are tall versions of eleocharis. E. vivipara comes to mind.