I have done this by writing a descendant of TRichEditToolBar but it would be a great addition to be able to add custom buttons to the toolbar.
Also exposing an array of the buttons/controls would be nice so styling/ids can be set. Maybe this can be done and I have missed something.
Nice features, I would like to see it too
You can access all controls on the TWebRichEditorToolBar via
WebRichEditToolBar.Controls
To hide a button for example, you could write:
WebRichEditToolBar.Controls[2].Visible := false;
To insert a button, you could create a new button and set the button Parent as WebRichEditToolBar