I always thought that gassing freebase cocaine wasn't a widely practiced procedure because the cocaine molecule was very vulnerable to strong acids and bases. That's why NaOH isn't used to basify the HCl salt. So just use the crystallization procedure that most people use for regular cocaine freebase.
Post 442507 (https://www.thevespiary.org/talk/index.php?topic=9763.msg44250700#msg44250700)
(andromeda: "Cocaine Base to Hydrochloride Method", Methods Discourse)