I agree with all the other things mentioned, but if you really want to do this in Braze yourself, you could:
Trigger an event/attribute update to a 'fake' user - on that exists in Braze, but doesn't correspond to an actual user.
That will cause, for that user, a webhook campaign or a canvas with a webhook step in it...
... that triggers a campaign/canvas for the actual audience via the Braze API.
I'm not convinced this is the right way of solving your actual problem, but it could be made to work and would work reasonably well.
I'd be really interested in working on this with you if you'd like to reach out.