[Suicide Junkie]

Whenever I forget and end up with a 0-pop colony, I divert a second colony ship which is travelling nearby.

Orders:
1) Drop population on the empty colony
2) Load population from the empty colony
3) Move To/Colonize the original destination

Since you can't remove the last 1M pop, the above orders will result in a colony with 1M pop, and a colony ship with one less than max population continuing on to colonize.
This works great in simultaneous games, but is also quite handy for sequential when the trip is long. You can set and forget the orders.