I don't think that AskJeeves has such a switch - it is designed for the common user and not the techie. But the data comes from their Teoma spider [sp.ask.com], and they also just bought Excite and iWon, so we may be in for some changes soon.
Teoma is much more technically oriented and they do have a
site: switch. But you need to use at least one word in the search as well, not just a minus sign or a bare site:example.com
<correction> AskJeeves works the same as teoma -- you need at least one word. So for instance, this search get results: