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This is now possible, and the results are the "sought.cf" ruleset – an automatically-generated ruleset which seeks good rules directly from the SpamAssassin spamtraps, updated every 4 hours.Here are instructions on how to use it
Update: this is no longer active, and should not be used.
Gory Details
If you're curious, here is a technical explanation of the algorithm used, and here is an examination of their efficiency against our test corpora. Here are instructions on how it was used.