This forum item has a $5,000 answer (and a zero dollar answer).
http://psych.colorado.edu/~carey/Bouchard/BouchardPrize.php
Greg Carey is offering an economic stimulus package of $5000 cash to "the first person to demonstrate that C and E in the ACE model can act as legitimate variables in a causal model without the assumption that a specific, concrete environmental variable must correlate either 0 or 1 in siblings."