I as well have tried to get high from an aborted (posibly contaminated) pf-tek style mycelium cake. It didn't work for me either, it was years ago, but what I did (again, long time ago) was, crumble the mycelium into a mixing bowl, added a few cups of orange juice, mixed and let sit an hour or two,\. Then I strained off all the clumps and consumed the liquid. It was awful. Acheived nothing but an upset stomache.
I'd be carefull consuming things like vermiculite or partially bio-degraded rice flour. Also why did the mycelium cake abhort? Does it smell funny? I wouldn't eat some random fungus or bacteria that grows on the leftover macaroni salad in my refridgerator, If the cake is contaminated then there is something growing in there that is not what you had hoped for!
Eating mycelium cakes probably isn't a smart way to get high. And I don't know if anyone could tell you if its safe or not (we'll never know exactly what stalled the mycelium growth)
Edit: I dunno where I got the idea to soak in OJ, strain and consume. I probably read it off the net but psilocybin/psilocin is definetly water soluble (shroom tea anyone?). The stuff in the OJ may not have hurt,, but water would have been a safer (worse tasting) bet.
edit 2: apparently I got that idea from the shoomery! as Ason posted a link to the shroomery explaining exactly what I did. Makes sence this all happened in 1999 and back then the shroomery was just as useful/informative as today