[Suicide Junkie]

You're getting out of the intercept routine a time and a location right?

The ship should simply accelerate at the rate passed into the routine, and in such a direction as to end up at the returned location at the returned time.

That part is just another (Once for each dimension) application of the base formula S(t) = S(0) + Vt +A(t^2).

Within rounding error, the total acceleration will be equal to the acceleration passed into the routine originally.
(Don't forget Pythagoras)