You have a way to deal non-lethal damage to Vrondiss.
"Dragons" chosen with Outpost Siege.
Steps
Deal damage to Vrondiss.
Rite of Passage and Vrondiss trigger.
Resolve the Rite of Passage trigger, putting a +1/+1 counter on Vrondiss.
Resolve the Vrondiss trigger, creating a 5/4 Dragon Spirit creature token.
The Dragon Spirit enters the battlefield, triggering Scourge of Valkas, causing the Dragon Spirit to deal damage equal to the number of Dragons you control to any target.
The Dragon Spirit triggers, causing you to sacrifice it.
The Dragon dies, triggering Outpost Siege, dealing 1 damage to Vronidss.