Hi Will. Rhino has a "pipe" command which allows you to input many different radii anywhere along the curve. But i find it's rarely of much advantage over the sweep command. In most cases, Sweep is more useful because the inputs are reusable and you can set them up more accurately with reference to other geometry. Having a pipe command is only useful for doing simple things...

PS - Sorry for mentioning the "R" word !!! :)

jonah