In the older ovi maps (before pr 1.2), I was able to re route by doing something like repicking the start location as my gps position. Forgot the exact way since it's been a while.

With the latest ovi maps, it doesn't seem possible. It doesn't actually recalculate the route.

2 thing that might seem to work would be to just add a 3rd waypoint, let it calculate, delete it, then calculate again. Or change it to walking, calculate, then back to driving, then calculate.

Haven't actually tested these, but seems they will work. Not good while driving, but the newest n900 maps is horrible for driving altogether. Not really finger friendly, and haven't used it for a while.