Note that our 3 conditions,
1. Good outweighs evil;
2. Double effect is present;
3. No violations of rights,
are in full force in the trolley case. 3) exists for 2 reasons:
1. because I have no duty to do the impossible, namely save everyone;
2. because the 1 man presumably does not have a right to a track free of runaway trolleys. He knew the risks when he signed up for the job.
Thus, this case is analogous to Air in a previous post, and switching to track B is morally permissible.