Use AWS CodeBuild to test private components of a system deployed with CodePipeline

Question

I have a system that is automatically deployed by AWS CodePipeline. The deployment creates all resources from scratch, included the VPC. This system has some components in private subnets, which expose an API and have no public access. They are accessible from other internal components only. Once the deployment completes, I would like CodePipeline to start some API tests against these components.

I was planning to do it with AWS CodeBuild test action, but I have hit a roadblock there. The issue is that, to configure CodeBuild to run in a VPC, you need the VPC to exist. But my VPC does not exist yet at setup time of the pipeline.

Does anyone have a simple solution for that? Note that I don't consider create the VPC in advance, separately from the rest of the system, a solution. I really want my deployment to be atomic.