It is one of the possible solutions.

In combination with the "writable flag" solution, you might create a class
variable in IdleConf (e.g. "user_cfg") that contains the user's home directory;
such variable will be initialized to an empty string by IdleConf.__init__.
On each call, GetUserCfgDir tries to initialize "user_cfg" only if it is an
empty string, otherwise it returns it's content.

Anyway, keep in mind that in GetUserConfig there's an unhandled exception (AttributeError) that might be the cause of the "IDLE doesn't start..." issue reported by users.