I've done some work in catering and gourmet sausage production and a common practice is to use a hot water bath to get the internal temperature to whatever safe level is desired. Sausages can be held at this temperature throughout service without overcooking them or drying them out. When an order is received, they are finished à la minute under a very hot grill for only 1 or 2 minutes per side to brown & crisp up the skin and put on some nice grill marks (if that's appropriate for the style of sausage). Cooking them all the way through under intense heat (eg a BBQ or grill) will usually result in the sausages exploding and losing all the juiciness inside - this is a common mistake.
Sausages can be prepared this way either fresh or frozen, and by themselves or sealed in cryovac bags.
If the sausages are by themselves, it's also popular to use a dark stout beer (eg Guinness) as the poaching liquid. Temperature control of the bath is always key (it's basically a sous vide technique).
If the sausages are pre-portioned and sealed in cryovac bags, then the bags can go right from the freezer into a plain hot water bath for a pre-determined time, then the bag is cut open and the sausages finished as above. Obviously no need for beer or other fancy poaching liquids if the sausages are bagged.