Chocolate chips made for baking have a higher melting point.
The typical tricks used by chocolate manufacturers is to change the viscosity of chocolate by adding a gel like xanthan gum or glycerine. The other trick is to incorporate more water into the chocolate with the aid of an emulsifier such as lecithin. All these techniques are hard to do at home as they require many hours of stirring the chocolate to avoid grittiness. Patents often give recipes.
One can buy chocolate with higher melting points. Callebaut Volcano melts at 55°C, the highest melting point for a commercial chocolate that I know of, but is not yet on sale. Many of the commercial chocolate bars, such as the wartime Hershey's Tropical Bar use chocolate that incorporate these techniques as do the Nestle Toll House morsels.