I have just created a relatively modest bulge using a winding of thin electricians insulating tape, which I also use to finish off the wrapping at the shaft end. I think my opponents this evening will be intimidated by my bulge.
This is how I did with my BS-LYD using the Yonex AC380 cushion wrap, the original grip was peeled off and wrapped one layer of Li Ning GP35 with minimum overlap to create an almost flat surface...
The butt cap bulge is not as thick as what it is shown in Derrick's video but I think it should be enough just to prevent the racket from flying off and make a more solid base for the little finger to rest when i grab the racket lower. I did the similar thing just below the cap to fill in the gap where the wood handle slotted into the support cap.
The video from derrickn is very good.
But you can also use a strip of a towel grip around the butt cap and then putting you normal overgrip on it.
So you don't have to buy a special tape if you may have a towel grip strip at home