So you basically just want to track the 8 second HoT portion of CW then? Threw together a quick WA to do that, see below. Instead of using an Aura trigger with "Use Full Scan" or the Unit set to "Group" I just created an Event trigger that looks for a buff with ID 102352 being applied by the current player. An added bonus is that this will also track the buff if you cast it on an NPC or someone outside of your group. I only did a little testing with a combat bodyguard but it seems to work alright.
My Trigger:
Type: Event
Event: Combat Log
Message Prefix: Spell
Message Suffix: Aura Applied
Source Unit: Player
Spell Id: 102352
Aura Type: Buff
Hide: Timed, 8s
Code:
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