Carefully crack the case open using a knife. You can be quite rough at the PS/2 end of the casing as this part will be
removed anyway. Don’t destroy the USB side of the casing as this part will be reused for our adapter casing later on.

Once opened you should basically have a USB-connector connected to a PS/2 connector covered in hot glue/plastic wrapped in a thin-foil like material (for shielding). Remove the wrapping and cut away the PS/2 connector with a knife.

Now, carefully remove the remaining plastic. Don’t worry about the soldered wires but make sure that you don’t damage the pins on the USB connector. You should end up with something like this.

Do the same with another USB-PS/2 adapter so that you basically end up with two USB connectors.
Bring out your soldering iron and de-solder the remaining wires from the connectors.

Place the connectors back-to-back and turn one of them 180 degrees so that it becomes “up-side-down”. If you don’t do this you’ll end up connecting the pins in the wrong way.
To make the pins touch each other you’ll have to bend them roughly 30-45 degrees. Solder the pins together.

Cut out a piece of wire and solder it to the casing off each connector. You can use the existing solder points used for the shielding/ground or create a new. Some flux will help a lot here.

That’s it for the connector. Next up is to creating a new casing using the existing casings. Unfortunately I forgot to take pictures of this process.
Take on pair of the two cases, take one of the two pieces and place the USB-USB adapter inside it . Make a mark on the casing approximately in the middle of where the soldered pins meet.
Cut at this point and do the same for the same half of the other case. Just do a rough cut and file the pieces until the adapter fits. Once the bottom fits, do the same for the top part using the bottom pieces as a template.

Place it in the new casing and pour some hot glue over it to make it steady. Glue the top on and it’s complete.

USB-USB female adapter in action.

Will it be as good as a commercial adapter? probably not. Will it effect data transmission? probably (depending on how good the solder joints are). Cheaper than a commercial adapter? yep (assuming you already have the parts needed and don’t factor in the labor )