I don't think you can split the chord in different layers on the same staff (unless there's some plug-in magic that I'm unaware of), however, there's a couple ways to achieve what you're wanting to do.

You can use the "Split Stem" Tool un the Special Tools Palette which will give your chord the appearance of two layers, but will all be in one layer.

You could also highlight what you're wanting to change, and copy contents from layer 1 to layer two, then delete the notes from layer 1 that you don't want in the chord and then delete the notes in layer two that you don't want. This will get you the chords in the layers, but it's kind of clunky.

You could also use two staves, make a split point, then move the contents of the left hand to layer two, show active layer only, and then copy and paste back to the original staff. 

Again, there are many ways to skin a cat... hopefully this can get your started.

The plug-in JW Staff Polyphony can do that (in the same staff). Use Layers -> Split.