Replying to Support Piece for Bass

any bass players here in ns? i need help. this is kinda my last chance :).

yeah well my bass teacher said that i should get a support piece so i could hold my thumb there while playing E string. he says my playing with E string lacks strenght and aggressivnes. well i have no idea how i should make/put 1. do i just glue it on? i doubt it holds like that, so there has to be another way, but i cant figure it out. and also should music stores do these kind of things or do i have to do it myself? i shouldve gone ask this week, but i kinda forgot :p. i have Fender precision bass, so i cant really hold my thumb on mics eighter.

(if theres something that you dont understand, ask me, i know i suck at english)