It sounds to me that the OP is looking for a compressor rather than an attack/decay effect.
OP: If it is a compressor you're looking for (you want to regulate the volume of your notes so your playing is smoother - rather than wanting to make fade-in string effects [which is what the Slow Gear and the like do]) then yes you should just practice more.
Most bassists do use compression but not to compensate for poor technique. It will come in time, be patient.
