I don't know of any work-arounds that would help you. And I sure understand your frustration. Every time we use the GPS (which is every time we travel) we can't believe how un-technologically advanced they are. We should be able to talk to it and tell it things - like:
Don't tell me when there is a large interchange ahead that I don't want to go on.
We'd really like to stay on the road along the lake even if we could save 1 minute by taking a different road.
We're pulling into a gas station, so don't worry your pretty little head about recalculating.