I know that not everyone uses this strat anymore, but i'm having trouble finding a consistent way of getting clipped into the elevator, rather than being pushed out of the elevator.

Here's my example of being pushed out of the elevator:

Here's an example from Shizzal of being clipped into the elevator:

In order to clip through you need to be saveglitched. Make sure you don't shoot any portals too close to you during the saveglitch, since that cancels it.