Is it possible to calculate aggregate of an aggregate in BigQuery?

Question

In BigQuery, is it possible to calculate aggregate of aggregate without using sub-queries? For example, Median of Max per user can be achieved by:

SELECT PERCENTILE_CONT(x, 0.5) FROM
(SELECT user_id, MAX(property) x FROM table GROUP BY 1)

If possible I would like to reduce this to

SELECT some_function FROM table

Reason for this request is to be able to integrate such queries into our BI tools. Our tools assume the source table is a fixed table and allow us grouping or filtering with dimensions. The initial approach requires a different sub-query definition for every filter and group by(ie. median of max per user per country).