while i personally only have experience with whole chewed morning glory seed...
the lsa alkaloids are highly unstable, and the longer you expose them to heat/air/light the more degradation you can expect. the erowid tek is full of inconsistencies and confusion, and reads like a "theoretical" extraction by someone compiling hearsay.
there is no evidence that the nausea component can be reliably separated from the trip component, and LSA itself is known to be a vasoconstrictor. this means that you must be willing to accept the full spectrum effects of the drug. do not naptha wash your seeds, because you will either A) lose a portion of alkaloids to degradation or B) consume naptha. do not extract with methanol unless you have a vacuum apparatus to remove solvent without introducing air/heat/light, methanol is poisonous.
LSA is contained in its polar salt form in HBWR/MG seeds, so a quick lemon/cold water extract is best, compared to just chewing and swallowing the whole seeds. if you get enough chemical in you, nausea is to be expected, however green herb will calm it slightly and the trip is beautiful after you purge.
i don't know about the acetaldehyde/LSH theory, but peppermint tea can soothe the tummy for sure.