The Rocket Scientist likes the turkey burgers on the grill, but I'm having trouble getting them done enough (it's poultry, you know) and still keeping them juicy. Any tips?

Unfortunately, no. I enjoy ground turkey in a variety of dishes like tacos, burritos, Bolognese, and meat loaf. But the problem you face is the exact reason why I do not make turkey burgers. Hard to grill evenly and stick to the grill something awful. And they don't take to steaming (steamed burgers is a Central Connecticut specialty. See Jane and Michael Stern publications for more details) like beef burgers do.

mix in some ground veal and pork and they'll grill up like a charm

Actually, I have no experience with turkey burgers. Is the fat content still pretty high (albeit probably half that of ground beef)?

How about frozen turkey patties? It gives it a little extra time...

Like the others said, mix in some ground pork. Also, add some apple sauce, maybe 1/4 cup to a lb. of meat. Make sure the grates are well-oiled!