you'd better ask in the InDesign Scripting Forum:
Before asking you should know good answers to the following questions:
1. How are the exact scale percentages for x- and y-direction?
Could you tell a uniform scale for every placed EPS? Or will the scale depend on distinct cases?
2. How would you tell placed EPS files that should be scaled from others that should not be scaled?
By a naming scheme perhaps. Or you could tell by a page range. Or…
3. Are the placed EPS files anchored in the text?
Inline anchored? Above line anchored? Anchored anchored? A mixture of all three cases?
If all these questions can be answered sufficiently, one could write a script.
But that's only a starting point…