BMW has a new one-piece, heated only comfort seat available. It is supposed to fit 2005-2010 RT's but I would verify to be sure.
Slightly lower than the standard.
Standard seat height: 820/840 mm
Comfort seat height: 785 mm
It's also a bit wider than the standard seat.
More info here - http://www.barrierobsonmotorcycles.co.uk/view.asp?ID=9