How do I hold a key down using SendKeys::SendWait?

How do I hold a key down using SendKeys::SendWait?

I want to hold a key down (send a key down event) to an application (say
the "w" key) while I do something and then release the key later (send a
key up event) using SendKays::SendWait. How do I do this?
If I just use SendKeys::SendWait("w"); it sends the key down and the key
up very fast back to back to the application.