Is it possible to simulate multi-touch mouse down events?
There kind of is. Your question says "simulate mouse-down events", that's what's being covered in my answer. I used an application back in 2010, and I'm pleasantly surprised it's still being updated, and supports Mountain Lion.

It's called Mac Auto Mouse Click, and it's pretty configurable. You can set it to click anywhere on the screen and remember the position, and execute a whole series of commands, including keystrokes. It's also fairly simple to use. Here's a screenshot:



It is however limited in that it can only perform simple mouse-clicks, here's the full list:


  
  Left Mouse Button Click.
  Right Mouse Button Click.
  Middle Mouse Button Click.
  Shift + Left Mouse Button Click.
  Shift + Right Mouse Button Click.
  Shift + Middle Mouse Button Click.
  Double Left Button Click
  Type Text Automatically, like a Mac Auto Typer.