What about under-carpet flat-wire by Tyco? It's been about 10yrs, but I've installed it before. You put a large strip of special tape down, then the flatwire and finally a sheet metal type of cover.
http://www.ampnetconnect.com/documents/UC_Power_System_Presentation_Rev4_Web.pdf
I. General
324.1 Scope. This article covers a field-installed wiring
system for branch circuits incorporating Type FCC cable
and associated accessories as defined by the article. The
wiring system is designed for installation under carpet
squares.
324.12 Uses Not Permitted. FCC systems shall not be
used in the following locations:
(1) Outdoors or in wet locations
(2) Where subject to corrosive vapors
(3) In any hazardous (classified) location
(4) In residential, school, and hospital buildings