The following VBA example creates a blend and attaches it to a path.
Sub Test()
Dim sPath As Shape, s1 As Shape, s2 As Shape, eff As Effect
Set sPath = ActiveLayer.CreateCurveSegment(0.6, 4.5, 7.8, 8.5, 5.2, 62, 5.3, -96)
Set s1 = ActiveLayer.CreateEllipse2(0, 0, 1)
Set s2 = s1.Duplicate(8, 11)
s1.Fill.UniformColor.RGBAssign 255, 0, 0
s2.Fill.UniformColor.RGBAssign 255, 255, 0
Set eff = s1.CreateBlend(s2)
eff.Blend.Path = sPath
eff.Blend.StartShapeOffset = 1
eff.Blend.EndShapeOffset = 2.5
End Sub