Ugh. Lop.com is a pain. If your comp has been raided with it's garbage, you can get the uninstaller from http://lop.com/help.html#how
Otherwise, I'm pretty sure that's impossible. You could do it with ActiveX I'm sure, but that takes a lot of know-how that I lack
It would also be a security hole, unless it prompted the user like the "set as homepage" thing does.