Unique logo per page or blog

Hi,

I am currently using a logo image set in the site settings.

As I have more than one blog on here for different people, I would like to be able to change this logo image to a unique image per blog page. How can this be done? See two separate blogs here:

http://shane-lord.squarespace.com/

http://shane-lord.squarespace.com/imogens-blog/

I would like a different image on Imogen's Blog.

Thanks, Shane.