extending the authorization system

I am developing a module for integrating an open source ajax chat into EE. For this purpose I want to rely on the EE authorization system to log users into the chat and define their access rights. To accomplish this, I need three additional tables, one that assigns a predefined role to each registered user, a table containing a list of chat rooms, and a table that defines who has access to which room.

Now, implementing the tables is easy enough, but I ran into a problem: the exp_member table in EE relies on the MyISAM engine. This means that I can’t use foreign keys in my table to define a relationship between users and roles (this is only possible with the innoDB engine). This also means that I can’t ensure consistency in my new tables when users are removed from the exp_members table.

I could write a small extension that on removing a user in EE also removes the entries for that user in the chat tables, but then I would have to deal with an extention AND a module.

I could also write a cron job to execute a periodical integrity check and remove users from the chat tables that have been removed from the exp_members table.

Neither approach is particularly attractive to me, so I am wondering:

is it possible to implement the extention as part of the chat module? Are there any other ways to ensure the integrity of the chat tables?

Thank you for your help,

Franco