The 2003 version had a wonderful Macro recorder. I still keep a copy on a virtual machine and use it quite a bit.
I can write the VBA for you to do this.
When you say. Manually select. Is that all objects on the slide or just certain ones?
for the center? is this a text alignment? Maybe it's shape alignment and you want to center them all in the center of the slide?

Just need a few more specifics and I can jam this VBA out for you.