How about simply putting another picturebox inside the 'nice viewport', set it's AutoSize property to True and BorderStyle to None, and run code something like this:

(picViewport is the large picturebox with the border you described and picImage is the actual image)

Code:
picImage.Picture = LoadPicture("C:\Blabla.bmp")

With picImage
    .Top = (picViewport.ScaleWidth - picImage.Width) / 2
    .Left = (picViewport.ScaleHeight - picImage.Height) / 2
End With