You actually don't need to register a .net assembly if it's hosted on a web server, you can just use the overloaded <OBJECT>
tag:
<OBJECT id="Obj1" classid="Assembly.dll#Full.Namespace.ControlName">
See http://support.microsoft.com/kb/317346:
This usage is very powerful, because .NET assemblies install by using the new zero-impact Fusion technology, which enables assembly installation without the need to write any secondary information to the user's registry. To update the control is as simple as downloading a new copy (which the Runtime takes care of automatically); removing it from the computer is as simple as removing the assembly from the Fusion download cache.
Also see: How To: Deploy COM Interop Programs to Internet Explorer