Not easily perhaps, but possible.
This query “works” in Data Explorer (Admin only)
SELECT users.username
, user_custom_fields.value
FROM users
JOIN user_custom_fields
ON users.id = user_custom_fields.user_id
OR users.id = CAST( user_custom_fields.value AS int )
WHERE user_custom_fields.name LIKE 'shadow_id'
ORDER BY user_custom_fields.value
example results
username value
AdminGuy1 35
anonymous 35
anonymous1 36
LeaderGal1 36
anonymous2 37
LeaderGuy1 37
SpamGuy2 38
anonymous3 38
BasicGuy1 39
anonymous4 39
TrollGuy1 43
GothGal1 46
anonymous5 46
* the “anonymous” for TrollGuy1 is missing because the post was deleted.