If you are authenticating with LDAP you could set up secondary IDs for the users with greater access in DE. You could easily schedule those ID's to be disabled in AD during the week and enabled for the weekend. Of course then your users need to remember to log in with different ID's on the weekend.
Alternatively...
This is not a solution that would ever be officially recommended, but you could write a SQL script that operates directly against the database to make changes the security groups individuals belong to. There could be any number of unforeseen issues that result, but the basic table structure doesn't look that complicated.
This is not something I would personally try but then I don't have your need to modify security on a weekly basis, and I'm generally risk adverse. If you end up spending a weekend restoring your environment from a backup, don't blame me.