This announcement went out this week: https://circleci.com/blog/introducing-circleci-api-v2/
You can now trigger pipeline first class and use parameters that can be resolved at trigger time (meaning you can use those variables anywhere in your config, effectively, not just in job steps). This would require some tweaks to your config.yml, but we are encouraging everyone to start using the new triggering API in v2 as soon as practical.
We are hoping to get everyone using the job triggering endpoint in 1.1 to move over in the next couple of months. If that will be problematic, don’t panic, but if you foresee a problem do please reach out here or to your account team at CircleCI if you have one.