I followed this blog post to set up domains for WordPress Multisite. My only problem is that all images are uploded and served from main domain.

Do you know how should I set it up that images uploaded from secondary domain will be uploaded to and served from secondary domain?

I also asked this question on Stack Exchange:
http://wordpress.stackexchange.com/questions/163426/why-are-images-uploaded-to-main-domain-when-using-multisite-with-different-doma