Wet Okole seat covers (neoprene) did the (static free) trick for me! The workmanship on their product is excellent, and they are vehicle specific constructed to allow for safe airbag (front seat) deployment. My 2011 Leaf did not come with heated seats (they were not available at that time), but I bought front seat heaters (also from Wet Okole) for both front seats (powered one at a time via the accessory power outlet) which are just under the seat covers. However, I note that both the 2012 and 2013 Leaf Owner's Manuals have this seat warmer warning (~p. 2-47) that relates to seat covers in general:
"• Do not use the seat heater for extended
periods or when no one is using
the seat.
• Do not put anything on the seat which
insulates heat, such as a blanket,
cushion, seat cover, etc. Otherwise,
the seat may become overheated."
So you need to take this into consideration when buying seat covers, i.e. together with the original seat covering do additional seat covers insulate the seat heaters too much?