Electrical tape or nail polish both work great.. Although you don't have to worry about the nail polish rubbing off with time as opposed to electrical tape..
Playing with a lighter touch actually facilitates faster speed and better endurance.
Whilst playing slap-pop, it's rather difficult to play with a light touch unless you play with a follow through motion with your thumb.. So proper technique or change in technique is probably a good idea if all else fails..
Also - Be careful not to bring the pickups too far away from the strings.. The farther away the pickups are from the strings, the weaker the signal.