Ok, I asked a friend of mine, who asked a guy he knows in Peru.

He says that camalonga seeds are used for protection.  People do not eat them, because they are poisonous.

He says there are some shamans who use camalonga to heal, but they NEVER eat the seeds by themselves.  These shamen only use camalonga, nothing else.  They macerate the seeds in an alcoholic drink made from sugar cane and drink the juice in order to heal people.

The seeds do contain strychnine.  He thinks that the fact that they macerate (=soak) whole seeds but do not crush or grind them is important for ensuring that the concoction is edible.  Anyway, he does not recommend trying it.

Nevertheless, this makes me think that strychnine is not present in the drink in any significant amount.  Overdose would surely be common otherwise.  I would guess that there is either another entheogenic chemical in the seeds which enters the drink, or the drink is not chemically active.  Perhaps the fact that the seeds are poisonous adds mystique to the shaman's work?