A fully customisable google+ comments plugin for your WordPress blog.
For non-responsive sites where width is fixed, you can set the width to the width of your comments container. For responsive sites, the width will vary depending on the screen. In this case use the "Dynamic Width" option which will calculate the width and add a plugin with that width. It will work fine if you use "Dynamic Width" for a non-responsive site, but with the fixed with, an extra calculation can be avoided.
Unfortunately, Google has not yet made this feature available in the commenting system. It will be made available in the plugin as soon as Google releases the feature.