How do I skew Drawing Canvas?

Hi

So I wanted to make some simple shadows in a top down style game, and thought I could do this using the Drawing Canvas object, grabbing the objects I want to cast a shadow for, painting them black and lowering their opacity, before skewing the objects and drawing them to screen.

Most of this is easy enough to do, but I'm struggling to skew the objects before drawing them. Reading through the manual, I'm not even sure if this is possible, but thought I'd ask anyway.

Here's a mockup of what I'm hoping to do with the shadows:

I used that effect in my game, it's pretty good and really makes the characters look more alive.