Well, I'm not sure if this is exactly what you are working towards, but it works for me. This does have a bug, but it is the easiest way I've found so far for me.
I went to Google Maps in my browser, selected 'LABS', and enabled the 'Short URL' feature. Then, after I build my directions on the Browser, I select the 'Link' button in the top right of the Map. I then send this short URL link to my phone and it prompts me to open the link in Internet or Maps. So, I select Maps, and my phone launches Google Maps and goes directly to the directions where I can just select 'Navigate' if I want to. And, this includes the way-points I set in Google Maps in the directions on the phone too.
The bug is, that the short URL doesn't seem to be a 'static' link since when I close the desktop browser, the short URL link stops working. But, once I have the directions up on the phone, who cares.