You can vacuum a limited number of tables manually in every few hours. Set a cronjob to 1. collect say 50 tables with oldest refrozenxid into a file. Append each tablename with vacuum analyze to make every line a psql command to vacuum each table. Then input this file to psql.
Say you run it every few hours, each time it is run, 50 (in this case) oldest tables will be vacuumed. This way you can maintain the tables without overloading your server or generating excessive WALs all of a sudden.