Simplifying the commerce UI for clients

I'm building a multiuser marketplace using the MarketPress plugin and I was wondering how to achieve something a bit more simplistic than the current implementation.
To be more exact, all the stores on my network will be from the same country, will have the same taxes, same payment methods, same shipping quotes etc.
So there is no real need for all those options to be present on each site. I want the superadmin to be able to change those on a network level, not per site.
The trick is that the users will be TOTALLY clueless and their only interest is adding a few products on each store. Any extra options will get them dizzy (and in turn I'll probably kill myself from all the questions they're going to ask me).

I want users to have no options except their paypal address and a few more basic fields.

Has anyone thied something similar or have any ideas on how to achieve this?

I know that I could "hack" the plugin to declare some predefined options and then hide (css) all the unnecessary options from the admin UI but hacking core makes maintenance and upgrades a real nightmare. It's a really quick-and-dirty solution and I'm looking for something a bit more permanent and elegant than that.