Lightroom :: Rotate Without Losing Some Of The Image?

I used a flat bed scanner to scan in a bunch of old photos.  The photos aren't completely straight -- I figured I could rotate and recrop using LR.
 
Here's the problem: I have a bunch of crooked photos on a white background.  If I try to rotate the photo, it ends up cropping out part of the photo.  (This does make sense -- You've all seen this when you've tried to rotate a photo.)
 
But I need to figure out how to tell LR to just add in extra white background where needed instead of cutting into my actual photo.
 
I can do this in PS by creating a big white background, rotating the original pic and then cropping.  That's a hassle when you have 100+ images.  But isn't there some way to do this in LR?