See the new "What Film Popular In The Year" spam post. All that would be required would by a succession of dichotomous keys to catch it:
1) Is this the first post under a new username?
2) Does the post contain known keywords e.g. keto, gummies etc
3) If not the first post under a new username, has there been an earlier post under the same username in, say, the last 30 seconds.