How to create ArcGIS Toolbox built-in tools using ArcObjects?

Hello - I am in a situation where my Python arcpy scripts are limited (the arcpy API is limited I should say) so I can't create a satisfactory script tool and I can't use a model to create a tool I want because some of the things I need aren't found in the Esri built-in toolboxes. That leaves me with needing to create my own tool using ArcObjects and making that available in my toolbox as a custom built-in tool. My problem is that I can't seem to find any documentation that tells me how to take my ArcObject classes and make them available as a built-in tool that I can add to my toolbox. I hope I explained that coherently. Any thoughts on how I may go about doing this??

Thanks - Peter