Merchandising Variables in Calculated Metrics

Suppose I have a variable that captures fulfillment method--call it evar1:

Because items in the same order can be fulfilled differently, I've opted to make evar1 a merchandising variable. That way, each order item attributes revenue to the correct fulfillment method.

I then make a hit-level segment where evar1 = Store Pickup. When I show revenue for this segment, I get a different number:

This is because the segment looks for hits that have at least one Store Pickup item and pulls in ALL the revenue from those hits. Since Store Pickup items are sometimes ordered alongside Truck Delivery and/or Parcel items, the segment also includes some revenue from those fulfillment types.

I want to make a calculated metric: Store Pickup revenue / all visits to the site. I only want Store Pickup revenue, so I can't use the above segment in my calculation. But as far as I can tell, there's no way to directly use a merchandising variable value when making a metric. Is there a way to do this, or is it not supported right now?

Thanks for you help!