Yep, hwy 99 is the only choice. Well, that or helicopter.
I found "Alta Lake Road" that also runs north-south, but on the other side of the lakes which are to the left of hwy 99. Problem is, I've never been on this road so I dont know what it's like. Paved or gravel? Lots of car traffic? Extremely challenging or newbie-friendly?
Here's a visual of the area: (Yahoo Maps):
http://maps.yahoo.com/#mvt=m&q1=whis...0.106405&mag=4
If anyone out there can comment on this road, that would be great. Cuz as cuski says, the Sea-to-Sky ain't famous for being safe.
cheers!