B-Splines: BSpline class and BSplineElement class
[quote user="John Davidson"]The code I have used for all the other element types works fine because they have a fillmode hook, but bsplinecurves do not have that option[/quote]
While what you say is literally true, I suspect you may have overlooked the fact that there are two classes that concern B-splines.
The BSpline class is a wrapper around the mathematics of B-spline curves. It does not represent a MicroStation element and hence has no Fill capability.
The BSplineElement class represents a MicroStation element. It does have Fill capability.
The attached DGN example has examples of closed B-spline curves and complex shapes that are composed of B-spline curves. I can apply fill using MicroStation tools. I can create a grouped hole using MicroStation tools. I can apply fill to a grouped hole composed of B-splines using MicroStation tools.
VBA Element Class Hierarchy
BSplineElement inherits a number of properties and methods from Element. It implements the ClosedElement interface. The ClosedElement.FillMode property provides what you request.
Dim oCurve As BSplineCurveElement
... get B-spline curve from somewhere
oCurve.AsClosedElement.FillMode = msdFillModeFilled