PD9, custom screen resolution when windowed

I am hoping to configure a custom screen resolution for running Parallels Desktop windowed when recording training videos. I have found this, but it doesn't seem to apply to PD9, when I press + in that situation I can add printers and drives and such, but not screen resolutions. I am running an older MBP at 1680 x 1050, and I want to run my VM windowed at 1600x900 to downsize to 720p.
Am I missing something, or is there no way to add a custom screen resolution when running windowed?

Thanks,
Gordon