Hi Wouter,
I think you might be mistaken on what is actually happening with Google plus. It doesn't matter which account you use. What is being discussed is when someone is logged into G+ or their gmail account, the search results give bias towards sites plus'ed by the user and people the user has circled. Essentially, the idea is that if you or a friend have plus'ed something (essentially saying that it is valuable), then you will probably like that search result.
For example, you are logged into Google with whatever account is associated with your Google plus. I am in one of your circles and have given a plus to a certain website. When you search for something related to that website, it will likely show up in your results since you are logged in, but might not have shown up if you weren't logged in. Since I, who am in your circle, have plus'ed a page or site, it follows that we are friends and you may find it useful too.
So, if you can increase the number of people in your market who have plus'ed your page, content, and/or site, the likely hood of other people in your market (eg. their friends) seeing you in search results increases.