How can I remove a stuck heater plug

My Mazda Bongo (rf5c engine) was having difficulties with starting early in the morning so I traced the problem and thought it was definitely heater plugs as these are the major problem with diesel engines and cold start.

So upon replacement of the heater plugs, all of them came out easily except for one which broke and left the tip inside of the head. Now it’s a big problem because I can’t fit another heater plug into the opening as it is clogged up.

I have tried running the engine with only the tip of the heater plug and it idles as usual. To raise the revs and increase the amount of pressure pushing on the tip of the heater plug was another idea in my mind but it sounds very unsafe to me as the vehicle has a mid engine which is located right inside the van.

Does anyone have any alternative safe way to solving this problem