It is kind of possible in a kludgy way... I solve this by writing the image out at runtime and assigning it to the toolbar...
[code]
Dim lgBitmap As System.Drawing.Bitmap = TryCast(My.Resources.ResourceManager.GetObject(attr.LargeImage), System.Drawing.Bitmap)
Dim smBitmap As System.Drawing.Bitmap = TryCast(My.Resources.ResourceManager.GetObject(attr.SmallImage), System.Drawing.Bitmap)
CreateToolbarButton(toolbar, toolbar.Count, attr.Name, attr.Description, attr.Command, lgBitmap, smBitmap)
....
Public Sub CreateToolbarButton(ByVal toolbar As Autodesk.AutoCAD.Interop.AcadToolbar, ByVal index As Integer, ByVal name As String, ByVal desc As String, ByVal command As String, ByVal lgImg As Bitmap, ByVal smImg As Bitmap)
Dim button As Autodesk.AutoCAD.Interop.AcadToolbarItem = toolbar.AddToolbarButton(index, name, desc, "\x1b\x1b_" & command & "\n")
Dim lgImagePath As String = System.IO.Path.Combine(My.Application.Info.DirectoryPath, lgImg.GetHashCode().ToString() & ".bmp")
Dim smImagePath As String = System.IO.Path.Combine(My.Application.Info.DirectoryPath, smImg.GetHashCode().ToString() & ".bmp")
If lgImg IsNot Nothing Then
If Not System.IO.File.Exists(lgImagePath) Then lgImg.Save(lgImagePath, System.Drawing.Imaging.ImageFormat.Bmp)
Else
My.Application.Log.WriteEntry("Could not find large toolbar image for toolbar button: " & name, TraceEventType.Warning)
lgImagePath = String.Empty
End If
If smImg IsNot Nothing Then
If Not System.IO.File.Exists(smImagePath) Then smImg.Save(smImagePath, System.Drawing.Imaging.ImageFormat.Bmp)
Else
My.Application.Log.WriteEntry("Could not find small toolbar image for toolbar button: " & name, TraceEventType.Warning)
smImagePath = String.Empty
End If
button.SetBitmaps(smImagePath, lgImagePath)
End Sub
[/code]