In S&T export your route to a .GPX file. Then hook your Garmin to your PC so you have access to it's GPX file folder. Drag your .GPX file to the Garmin's folder.
Disconnect your Garmin and go into the tools and do an import route from the .GPX file. I'm doing this from memory so I may be slightly off on a step or two.
I use to do it this way all the time, now I do like others which is use S&T for the big picture, then load up the days drive in the Garmin by hand each morning using waypoints and end point. Just seems to work much better.