Preconditions and Postconditions - selective enable/disable

[Brother Bill]

Can we ship our application to Production with Preconditions 
enabled, but with Postconditions and Invariants disabled?  If so, 
how to?

This would allow nervous managers to still have Preconditions 
active in Production, with slower performance.  After 3 months of 
it "just working", they can disable the Preconditions for better 
performance.