There's a couple of things here.

1. The heat from boiling your cakes is destroying some psiloc(yb)in. Maybe not much, maybe a lot who knows.

2. There is no proof either way (yet) that toxins from contamination in fact get absorbed into the mycelial network. Some say the toxins are too big to readily pass through the mycelial network to the shrooms some disagree. Either way you're taking a chance, if there's contamination anywhere on (or inside) of your cakes you're playing russian roulette, as this way almost ensures that if there is contamination you will be ingesting toxins.

It's a perfectly good idea IF you are 100% SURE that there's no contamination. You might also try the cranberry extraction (it's somewhere around here) as this may help reduce the amount of psiloc(yb)in that is destroyed in your process.

Good luck, and be careful!