I believe in sort of a universal karma if a motorists has to wait for me 5 seconds them I am obligated to wait for a motorist for 5 seconds. If the delay I have to endure is greater then the delay to motorists I'll generally assert my place in the road (i.e. I'll hold a door open for one person but not for a whole bunch of other people (like at a concert)) but the 100' noted in the op sounds too late to go jumping into the lane sounds easier just to slow down a bit and jump in at the end of the pack of cars.