This is the only way I have ever done it
http://www.3riversarchery.com/3Rivers+Arrow+Weight+Tubes_i6731X_baseitem.htmlIt's simple for guys that build their own arrows, a bit tougher to add to a shaft with already glued inserts. However I have done it from the nock end when I do not glue in the nocks.
I actually don't glue in my nocks any longer so it's much easier that way.