[EDIT: Don't do this, as it may be against Google+ policies]
Creating a Page within your existing Profile
This option creates a Page for you, to which you can switch without logging in and out every time you want to switch to your anonymous identity.
1) First, go to your sidebar and choose Pages.
2) From here, you can click Create a page to begin setting this up. I've blacked out my anonymous identity, but you can see my Test Page here as an example.
3) For your category, choose Other.
4) Finally, choose your name and determine the appropriate age restriction for your Page.
To use Google+ as your new page, you just need to click on your profile photo in the top right.