Looks great.

Two requests:
1. Is there a way to enable it only for certain models? (Let me use it
on my legacy models, for instance, and keep my new models without it.)

2. How 'bout an option to generate the required code to stdout, instead
of just running it. So I could do:

puts LegacyModel.dry_sql_code

and get:
"set_primary_key 'lm_id'\n"
"belongs_to :xyz"

Useful for debugging, learning, and when you still want to retain
control (I have something similar to this in a rake script)