Customer events pixel checkout_completed and {{ first_time_accessed}} equivalent?

Is there an equivalent of {{ first_time_accessed}} for the new customer events pixel checkout_completed event?

It looks like the new pixels will not accept liquid.

https://shopify.dev/docs/api/pixels/customer-events#checkout_completed

Shopify Partner support confirmed to me that and equivalent for {{ first_time_accessed }} does not exist yet. This is pretty concerning. Seems like a huge oversight compared to previous expected behavior.