There is an exercise I was shown by Ed Rennie at a Devon Squeezebox workshop, I believe it is used by piano players.
Place your fingertips palm down on the edge of a table in front of you.Then one hand at a time drop first your ring and first fingers straight down at the same time, leaving the other two on the table edge, then lift them up place and them back on the table edge and drop the other two fingers together, repeat getting faster!! Difficult to describe and quite tricky to do at first.Then start doing both hands at the same time. Eventually try doing different sets fingers on each hand at the same time.According to Ed this makes the brain think separately left and right thus basses become easier, time will tell.