I can definitly see the benifit of that... the metafile would work great for
slides with large amounts of content on them.

I managed to hack together my own solution in VBA to automate much of it,
and I'll include the code below for anyone interested. It will copy a
selected image on one slide, create a new slide on a second presentation,
paste the image, and then resize/center it on the new slide.

The Setup: Ensure both presentations are open and onscreen
(Window->Cascade). Select the image you want to copy from the old
presentation, and run the macro. To copy the next image, reselect the
original presentation, move to the next slide, select the next image, and
wash, rince, repeat.

The Code:

Sub copyImageAndResizeForHeight()

‘yay variables
Dim oView As View
Dim oTargetPres As Presentation
Dim dSafeMargin As Double

‘copy the currently selected image in the original presentation window,
‘and then select the new, widescreen formatted presentation
ActiveWindow.Selection.Copy
Windows.Item(Index:=2).Activate

‘in the wide presentation, create a new blank slide
With ActivePresentation.Slides
    Set oView = ActiveWindow.View
    oView.GotoSlide .Add(oView.Slide.SlideIndex + 1, _
                                      ppLayoutBlank).SlideIndex
    Set oView = Nothing
End With

‘paste the image into the new slide in the widescreen presentation
ActiveWindow.View.Paste

‘The rest of this code resizes the image to make it the full height of the
slide
   Set oSh = ActiveWindow.Selection.ShapeRange
   Set oTargetPres = ActivePresentation
   dSafeMargin = 0 ‘alter this number if you want a margin above&below your
image
   
   With oTargetPres.PageSetup
          ‘resize
           oSh.Height = .SlideHeight - (dSafeMargin * 2)

           ' center
           oSh.Left = (.SlideWidth - oSh.Width) / 2
           oSh.Top = (.SlideHeight - oSh.Height) / 2

       End With
       
End Sub

I created a second version of this macro for instances where the image was
significantly wider then it was tall. In this case, it would resize the image
to fit the width of the screen. It's all the same except for one line,
changing:
oSh.Height = .SlideHeight - (dSafeMargin * 2)
to:
osh.Width = .SlideWidth - (dSafeMargin * 2)

Took me ~30 minutes to go through each slide all told, but it allowed me to
ensure each image was sized correctly, and kept the file size exactly the
same. If someone can find a way to automate the rest of it, all the more
power to them.

Thanks for the help/info Steve!