This should be possible. I use 2 gmail addresses and have 1 google+ account. I would try logging into google+ with the usual account that let you in, then going to "My Account" and "edit profile". Try switching or adding the 2nd gmail address to the email's shown there. This should make the new primary google+ email the one you have chosen. I do the same within gmail on my laptop and phone as well. I have my 2nd gmail account forward itself via IMAP settings over to my main account so I only have to have one open in order to receive all mails.
Hope this helps! Let me know if not, I have one other idea but dont have time to try it out first, I dont want to give you incorrect advice. To work first c# and .NET HOOOOOOooooooooooooooooooooooooooooooooooo!