Pushing build parameter up the chain

Hello,

I'm using TC 9.1.3. I have builds B1..BN that have a snapshot dependency on build A. Builds B* are derived from a build template and there are a lot of them. The template is not linked to Build A in any way. Build A dynamically creates a build parameter via service message when it runs. I'd like each Build B* to pick up the value of that parameter either as a newly created parameter during the build or by updating a parameter defined in the build template. Ideally, it is an env var parameter, but could be a config parameter. How can I do this? Thanks!