This seems to work. When I find a fic to test with, I'll see if I can use include_metadata conditionals to exclude books with an actual series.
Code:
[archiveofourown.org]
## Copy collections to series
include_in_series:series,collections
include_metadata_pre:
collections=~Exchange
Is there any good way to set the series index of specific series to 0.00? I have a feeling this would be something better handled by the Action Chains plugin, so not a big deal.