Segmenting migrations based on target environment

I am developing against an existing database schema that I am enhancing
with some custom tables.

In the development and test database, I have basically generated
“copies” of the legacy tables that already exist in production. So I
have 12 migration files, some of which create dev/test versions of
production tables and some of which create tables that will need to be
moved to production since they are new.

I would like to have a separate set of migrations for the production
platform which is a subset of the set of migrations for my dev/test
platforms. Is there any built-in method for doing this with migrations
today (like some subdirectory convention, etc.) or do I have to roll my
own management scheme.

One simple solution I came up with was to compress my 12 migration files
into 2 files - 1 for the dev/test “copies” of legacy tables, and 1 for
the new tables that I’m adding. Then I just run the “new” migration
against the production DB.

But I’d really like to automate this so that I can have a capistrano
task that does migration as part of deployment to test and deployment to
production and have the migrations be correct in both environments.

Any migration gurus have any insight?