How do I add additional setup steps to services in Bitbucket Pipelines

I'm using Bitbucket Pipelines to run integration tests. I need to spin up a docker container to mimic the database so the tests can run. However, before I can run the tests, I need to add seed data to the database.

It seems like whether I add the mongo images as a service or add docker as a service, I still have to figure out a way to do the setup in the image from the script section of the default step, which is in a separate container.

That seems like a lot of unnecessary work, so my question is, is there an easier way? 

For example:

image: dotnet

pipelines:
  default:
    - step:
      services:
        - database
      script:
        - dotnet restore
        - dotnet build
        
definitions:
  services:
    database:
      image: mongo
      <it would be really nice if I could add setup steps here>