This may not be relevant to many, but it's a process that I just had to go through and it was a bit tricky to figure a smooth way to make it work.
The gist of it is that you must do the following:
- Export your production database from heroku to your local machine
- Create a new, blank database with Postgres 9.2 and PostGIS 2.0
- Import your heroku database into the new local database running 9.2/2.0
- Dump the new database and upload it to S3