Possible to stop the “manage themes” bit from admin area?

Hi,

I’ve written a program, that will setup a copy of WP for any user who wants it on my site. However, I want to have full control over the design (so I can put Adsense stuff on the pages, to make some money from the free service =)

Could someone please shed some light on how I could go about this? The user have “full” admin access to the WP admin area – so I need to really remove the option from the admin templates – as well as from the actual script itself (i.e if they try to be clever dicks, by going directly to the template editor URL :P)

TIA

Andy