I couldn't find this parameter in APNS options. Please add this functionality to admin console. For reference, description from your competitor:
content-available: (iOS only) If you are a writing a Newsstand app, or an app using the >Remote Notification Background Mode introduced in iOS7 (a.k.a. "Background Push"), set this >value to 1 to trigger a background download.
Thank in advance, although that option is missing, your servise is awesome.
This feature is under development, as I know it will be released in 1-2 weeks.
So, stay tuned with quickblox blog http://quickblox.com/blog/
It will available in Admin panel and through API as well
UPDATE
QuickBlox rolled out this update, check this feature in https://admin.quickblox.com