How can I programmatically re-enable a toolbar?

Here's the scenario:
1. User installs my toolbar into MSIE
2. User disables toolbar inside MSIE by right-clicking on toolbar and
un-checking it
3. User can't figure out why toolbar is gone, re-installs
4. Re-installation doesn't help, user calls and complains.

So I would like my toolbar installer to be able to (1) detect that the
user disabled the toolbar, and (2) re-enable it if so.

(1) seems reasonably straightforward, I look in [HKEY_CURRENT_USER
\Software\Microsoft\Windows\CurrentVersion\Ext\Settings] and see if my
toolbar's CLSID is there. That works.

But then if I delete my toolbar's CLSID from [...\Ext\Settings], the
next time I run MSIE, my toolbar still isn't re-enabled.

For what it's worth, during development I run MSIE 8 under XP.

Is this some security thing, that prevents me from programmatically re-
enabling a toolbar? Is there some API I need to call, instead of
directly manipulating the registry? Some weird authentication token
thingy?

Thanks,
Chris