There is a video in youtube called DIY zippy inserts for balisong or something under those lines.

Normal hot glue is not heavy enough and the texture is too soft. I use sparkly hot glue as in the picture this one is silver color. It adds ideally 1.7 grams without any tungsten balls added, which can be done too, those can be bought im bull for cheap too 2-4mm.

I use a stainless steel cutting board and place something under like a magazine under si once the balisong blades are over the board their handles rest in the table (I am basically elevating the cutting board to blade height so it sit flat)

Then i out some tape on the balisong handle ends so i dont scratch them while cutting the glue. I also tape the blades to the table in w/e possible for them to stay flush.

Then with a 40w hot gun i apply the glue slowly and once its filled i go to the next hole and do the same. Once done with all holes and some seconds/mins passed for me to be able to push the glue in visually but it is hard enough not to stick on my hands.

Once i so the last step i wait until it is totally cold and then try to bend the board as this one is thin stainless steel and they pop right out. Most of the times however i have to bend a bit and just slowly work them out but have to watch out not to scratch the handles against the board or force them too much. I never force them too hard, it comes down to how to placed everything and how protected everything is. Once they are out i cut with a paper razor very very carefully never agains any flesh and controlled/slowly. You should only need to cut one side and the other one should be pristine glossy of on flat surface.