How To Hide Columns In A Bound Gridview With No Rows

I've got a grid view on my form that is bound to a data table at run tim. The data table is returned by a function rather than direct from the DB so I can't set the datasource at runtime.

I bind the grid in the page_load event like this:-

Code:
Dim _dt As System.Data.DataTable
_dt = _srvc.GetVinylShutters(0)
_dt.Rows.Add(_dt.NewRow)
grdShutters.DataSource = _dt
grdShutters.DataBind()
(_dt.Rows.Add(_dt.NewRow) is just there to add a blank row in, otherwise I wasn't seeing any columns at all)

I've then got the following snippet which I want to use to hide some underlying columns:-

Code:
For Each col As DataControlField In grdShutters.Columns
Select Case col.HeaderText
Case "OrderID", _
"ShutterID", _
"ModelID", _

[Code] ...

The thing is, wherever I put this it doesn't seem to hide the columns. If I break into the code I can see that grdShutters.Columns.Count equals zero althought I can see that the bound datatable has 38 columns.

I've tried the Page's Load, LoadComplete and PreRenderComplete events as well as the gridview's DataBound, RowDataBound and RowCreated events. I get teh same result in all of them. The grid doesn't actually have any columns until it appears on the screen.