Extend Lollipops "heads-up" notification duration

Been trying to find a way to create a persistent heads up notification, exactly like receiving a phone call or hangouts call. Are these restricted to Google/system apps?

I've tried:

• Updating the notification before the heads up notification is removed.
• Setting the ongoing flag to true.
• Setting auto cancel to false

Can't seem to find this being done anywhere.

It worked for me:

• set ongoing flag to true
  
• set full screen intent
  
• set priority to PRIORITY_HIGH
  
• set category to CATEGORY_CALL