[Dovecot] Custom sql query for keeping quota with dict-sql

Hello! I'd like to setup quota for for virtualusers, i'm using both maildir++ and mdbox as storage, and i'm using postgresql to keep users. I'm keeping all users data in one table: [...] login text NOT NULL, domain text, password text, quota_mb integer NOT NULL DEFAULT 0 [... other columns ...]

i'd like to keep present quota in such two columns: quota_dict_bytes integer NOT NULL DEFAULT 0, quota_dict_messages integer NOT NULL DEFAULT 0

I read wiki a little and it looks i can't define own sql queries, they appear to be hardcoded. Am i wrong? Is it possible to write own queries to get/set quota using such table schema? Or maybe there is diffrent way to track quota for diffrent storages?

Regards! Marcin