You're not missing anything, there's no way to call ConfiguratorB from ConfiguratorA.
What it sounds like you have already figured out is that if you choose B, you can go down a different/additional route within A - that's the best way the product can handle what you're looking to do. But, again, you're right in that you've not got two bits to manage.
I think have a 'Add Configurator' button here, would do the trick.
That would be an awesome addition in future updates. I just didn't know if it was available currently. The more I work with building product bases in this software, the more I see things I didn't before that help us personalize it to our workflow which is deeply irregular to begin with so the concept that I had somehow overlooked the ability wasn't outlandish. Thanks for the help Matt!