Formulas: Reference parent item column from sub item formula column

Example:

WHEN {PARENTITEM_TRIP_TYPE_COL} = “MY_TYPE” ADD PARENTITEM_SUBITEM called “DINING RESERVATION” SET SUBITEM_DUE_DATE to 30 days before PARENTITEM_TRIP_START_TRAVEL_DATE

I have the formula to take date 1 and set date 2 30 days before date 1 within an item.

SUBTRACT_DAYS({Start Travel},30)

I see in the link at the bottom of this post that you can reference a parent_item in a query.

So it would be cool to at least say:
MY_VARIABLE = RESULTS OF QUERY(SUBITEMPARENT_COL2)

Then run the date setting function on the subitem date field like so:
SUBTRACT_DAYS(MY_VARIABLE,30)

Or in a less hacky way:
SUBTRACT_DAYS({PARENTITEM_COLUMN,30)

Thoughts?

Reference Link: