I don't know how it works exactly in unigui, Farshad could say more on that...
But what must be done on the client? The client (browser) can only show HTML, so the new (visible) "controls" must be inserted as HTML code into the currrent HTML code using javascript on Client side. If there are 100, you must insert 100. But if this 100 are in a "container" you can produce HTML code for the complete Container and insert this (big) html part in one Operation.
Try to create a new Frame (TUniFrame) with the controls and then set .parent := form.