I wrote a while ago about Heston Blumenthal's method of simmering sausages in water below boiling point before frying them. It did not work for me; but possibly the temperature of my water was too high.
Blumenthal's was not a completely new idea. In French Provincial Cooking, Elizabeth David advises that you "stiffen" Toulouse sausages for frying or grilling by dipping them briefly in boiling water. Italian sausages have a similar, coarse texture. Valentina Harris, in her book Italian Regional Cookery (now out of print), gives a recipe for "Alvaro's sausages with beans": you put the sausages into the water with the dried beans for the last 15 minutes of cooking, again before frying them.
I am not convinced. Very gentle frying -- I allow sausages 30 minutes to cook -- seems to me to be the best way to retain their texture and tenderness.
That is my theory. But for some reason, it does not apply to barbecues. The heat of a barbecue is fierce; but a barbecued sausage is a lovely thing.