ProE creates curves by equation using a parameter t
t varies from 0 to 1 over the range of the inputs so that you can vary something line the angle by entering t*360 to get an evaluation from 0 to 360 instead of at a single point.
Basically you can take any equation interms of x,y,x and parametize it with t so that you can generate the curve intended. for a circle in the z plane
x = 4 * cos ( t * 360 ) (-4<= x <= 4)
y = 4 * sin ( t * 360 ) (-4 <= y <= 4)
z = 0
to make this a helix simply vary z such as
z=t*4 to make the height of the helix 4. (0<= t <= 1) and (0<= z <= 4)
to make a spiral add a damping function.
x = 4 * cos ( t * 360 ) *exp(-t)
y = 4 * sin ( t * 360 ) *exp(-t)
z = 4*t
Once you have the curve you need you can use it as the trajectory for your variable section swep. You can also use other types of curves as well if you can sketch your curve or create it as the intersection of 2 surfaces.