Step 1: Bullet
Get a good non-damaged* nerd bullet.
Damaged as in bent, punctured ETC.
Step 2: Mod
stick a straw into the the back hole of the bullet and then cut it so none of the straw is poking out.
Step 3: Enjoy
Enjoy your upgrade bullet and utilize it.
P.S. You might want to push the straw back in if it come a tiny bit out.