If you play through the true ending (the Clocker achievement), you can get both endings without having to do a full playthrough. Once you get the true ending, go back and select the last chapter. When the father gets to the part where you have to let the guy release extra water (so Alice can cross later), don't do it. The Alice will get stuck and not be able to get the missing piece to her father. Then the bad ending will trigger.
You obviously still have to replay to get the Safe Out and Talking Too Much achievements, but you can cut off at least a little at the end.