Reducing the noise in a rendering which uses HDR lights

I'm trying to render a scene in 3Delight using the default envlight
for lighting.  Unfortunatly it's adding a lot of noise.

http://www.eightlines.com/neil/temp/149.jpg

Is there any way to reduce the noise without increasing the samples
paramater?  I've increased it to 512 (from 16) and while it's okay
now, it takes forever to render (Over a half hour).