I know as an upright and electric player that many of us who double simply use our upright fingerings (1-2-3&4 together) for a lot of things on electric. It works fine and you can always throw the 4th finger in the mix when you need it. I know I see a lot of patterns bassists use that don't involve the 4th finger. It can be very helpful but certainly you can play your whole career without using the 4th finger that much. I know I did.