Well, I've implemented a wonderful new costs page.
There's a wonderful nrg/bp/cycle bit in the left column. Assuming you want bots to lean up on the DNA code, set the cost here accordingly.
The higher the cost, the stronger the selective pressure to maintain DNA brevity. Don't set it too high or you'll place a higher pressure on DNA brevity than on important things, like efficiently finding food.
A good value might bo something like .005 maybe. I dunno, that would charge a bot with 200 DNA bp 1 nrg per turn.