Were you thinking along the lines of SendStringToExecute?
I tried the following but it didn't work either:
Dim acadApp As AcadApplication = CType(Autodesk.AutoCAD.ApplicationServices.Application.AcadApplication, AcadApplication)
Application.DocumentManager.MdiActiveDocument.SendStringToExecute("Test" & vbCr, True, False, False)
Dim startPoint() As Double = {100,100,0}
Dim endPoint() As Double = {200,200,0}
acadApp.ActiveDocument.ModelSpace.AddLine(sp,ep)
Above puts the line on the wrong layer.
Is there another method you or anyone else can think of?