Hi [USER=147757]@twiggs462[/USER]
A forum member may mump in with scripting capabilities with a good answer.
I did not try and run the script yet; sometimes, trying to put something under a Background Layer could throw a fault.
This could be done with an action, too.
Here are the verbal steps, and I assume this is a pixel Layer and a single Layer. Modifications could be made to cover those cases, too.
1) Make sure all selections are turned off
2) Make the background Layer a regular Layer
3) Duplicate the single regular Layer to the Second Layer
4) Transform the second Layer and rotate 90 degrees
5) Use the Image > Reveal All command and you will have boundaries that are now 1:1
6) Delete that Second Layer
7) Add white Layer at bottom
8) Merge back to single Layer
9) Save As file
Now you use the File > Automate > Batch command to access a folder of images and run this Action and use the Override Save As with your options as chosen in the Batch command
This was a quick write up yet this should work
Hope this was worth considering (avoiding scripts is worth considering)
John Wheeler