How to promote without being evil..

I floated the idea of running a weblogs inc kinda banner at the top of each blog to promote the service but have so far found no takers (quite the opposite :o)

So I was wondering how, given the multitude of themes available (I’d be wanting to insert this into each theme…) and a kind of goodwill feeling that people wouldn’t delete it once they can edit their own themes, I could best promote through edublogs blogs without pissing people off.

Any ideas?