You can do the following:
Dim cssHolder As Control = CType(Me.Page, DotNetNuke.Framework.CDefault).FindControl("CSS")
If Not (cssHolder Is Nothing) Then
Dim cssLink As New HtmlGenericControl("LINK")
With cssLink
.ID = "SOME_ID_NAME" & CStr(Me.ModuleId)
.Attributes("rel") = "stylesheet"
.Attributes("type") = "text/css"
.Attributes("href") = Me.ResolveUrl(SOME_CSS_PATH)
End With
cssHolder.Controls.Add(cssLink)
End if
that should work just fine,