I don’t think it’s possible to do what you’re suggesting. The PIE machinery uses the same machinery involved in saving games.
I think what you’ll have to do is create another system for managing this large amount of data. Instead of an array variable you would store some identifier that you can use to retrieve this information.
With a separate system you should be able to set it up in such a way that it is preserved for PIE but ignored for serialization.
Edit: On second thought, I’m sure there is some way in PIE mode to locate the other world context that you originally generated the data in. Perhaps then you could override PostLoad() to detect PIE mode, look up the original actor, and reference the same data.