In the current version the only way to add user and custom controls is by modifying the Web.config file.
Look for the following tags <telerik><cms><toolboxControls>.
Example for user control:
<add name=”MyUserControl” section=”My Controls” url=”~/UserControls/MyControl.ascx” description=”Some description goes here” />
Example for custom control:
<add name=”MyCustomControl” section=”My Controls” type=”MyControls.MyControl, MyControls” description=”Some description goes here” />
In beta 2 we will provide the ability to upload controls from the user interface and configuration will be handled automatically.
Note that there are still some problems with the design time handling of controls but they should work fine at run time.