Allow user to choose from a dynamically build option menu in a workflow approval step

We are using CircleCI to build docker-based multiple-repo feature-branch deployments. This process includes using the primary repository associated with the pull request triggering the circleci workflow. This workflow includes a docker build step that fetches git repo content from a secondary repository as it builds the docker container.

Normally, we just fetch content from that secondary repo off of its master branch. However, there are occasions where we’d like a manual workflow step that would allow a user to choose a different branch to use in the docker build step. Is it possible to build a drop-down menu in the manual approval process for the user to choose among a set of dynamically fetched options.