A friend uses a hairdryer with a homemade nozzle.
The nozzle restricts the airflow so it gets pretty hot but so far the hairdryer hasn't died or exploded.
He cuts a V in the back of the crack with a Dremel and then uses the hairdryer and some sticks of ABS to fill the V, much like you would when welding steel. I do like the idea of melting a piece of metal across the crack to reinforce it though.
That wavy design would negate the need for the metal to bond with the plastic.