Zdánlivě stejná odpověď, ale zatímco podporovatel může být ve vztahu k okolí i pasivní (fanoušek), nutně "nevnucuje" značku dalším lidem, propagátor jedná aktivně, o což dle mého v tomto případě jde - jinými slovy zvyšovat povědomí o značce (jak ostatně píšete).

Případně i "inovátor vnímání značky", ale to už je trochu delší a možná krkolomnější.

"...setting up an internal brand catalyst team to guard the brand story and to innovatively look for ways to embed it into the culture."
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"Brian Kagan, Brand Catalyst, Wizard of Wonder[ing]
Brian brings three decades of experience in the areas of secular product development, retail and professional services and branding for institutions and entertainment figures and companies. In addition, he brings a decade of experience in the faith-based environment. Brian has repeatedly demonstrated his capabilities by helping organizations both small and large refresh and often reinvent their brands while upgrading their public image. Brian has built his successful career by focusing on what he refers to as Brand Convergence: the bringing together of the core elements pivotal to sustained success for any integrated branding initiative."
http://www.changeffect.com/media/docs/WhatWeDo.pdf