FWIW I just installed a 27.2 Suntour suspension seat post on my RW4. I used a 30.8 sleeve (the bike shop didn't have a 30.9 sleeve) for the 27.2 seat post and it's working fine. I've put about 30 or 40 kms on it and it is holding position. I'm not sure why Rad's web site says the Suntour seat post isn't for the RW4 as they simply need to have a few sleeves in stock.
It works excellently. Very enjoyable riding now.