how do I cook sausages without poking holes through them?

If you are charring the outside then you are cooking the sausages too fast. Sausages are best when cooked relatively slowly: on a low pan, or under a medium grill. 20-25 mins in a 200C/400F oven usually does the trick as well.

I find that boiling the sausages first (in beer or water) until they are cooked, then lightly searing the outside with a little oil in the pan is the best way to cook sausages without splitting the casing.

This is the trick to sausage. Your want to cook it slowly, evenly, for a longer time. If you blacken the sausage casing while the inside is still raw your cooking to fast.

In a fry pan, turn the heat down to just above the point where the grease "spits" and cook for 30-45 mins.

In an oven, 350 F for 45-60 mins is a better bet then higher temperatures.

On a grill, the trick is to let the coals get to the "glowy" phase then add a pan of water to the grill. The water will help regulate the temperature Cook the sausages around 350-400 F for 40-50 mins. Remember to use the dampers to control the temp on a large scale. The water is an awesome trick to help control the temp spikes, and to keep the temp stable.

When boiling sausage (yuck) a high boil for over 90 mins is what I have done. But I don't like it so I don't have a lot of experience in doing it.

You can also cook sous vide at (pork at 60C) for about an hour, then finish on grill or in pan. No poking necessary.

Buy Skinless or cook in two way grill, ie., George Foreman type of grill.