GridMarket multisite secondary header

So I am getting along pretty well with my website project. You guys have been a huge help. I have another thing I would like to implement in my site. Im using multisite, GridMarket theme with a template. I want each users shop to look the same with my header image, however, I also want the user to be able to upload their own logo or image in their shop just above where their product is displayed. Any suggestions?

I purchased the MarketPress FrontEnd plugin and will be installing it soon, so if this option can be done in the front end as well, that would be great.