Work immediately in the flame without preheating the work surface. These metals melt at approximately the same temperature as the rod, so simply melt the rod in with them. Of course this means it is very easy to reduce your work piece to a molten lump, so great care is required.
When rebuilding pot metal, sometimes best results can be obtained if you prepare a container of moist sand to hold and position various items and to act as a former.
Small tools such as dental picks are useful for mixing the base metal with the HTS-2000. Before attempting repair of real items, some time should be spent practicing on scrap pieces.