I've made a USB dongle in transparent resin. The technique used is resin casting by using a silicon mould. That's the list of items and tools used:
-USB dongle, best a old one the first time, due it's a bit of risk to damage it.
-LEGO pieces to make a shuttering for the silicon mould.
-Modelling paste or any sculpture paste.
-Rubber for moulding, silicone. You can find it in some shop of toys, RC modelling, handcraft modelling or similar. I've bought it in a Spanish site called Feroca
-Transparent casting resin. Also you can find it in the same place than the silicone.
-Some system to measure the quantity of silicon, resin and catalyst. I've used a plastic glass and a syringe to calibrate the glass in ml and to add the catalyst.
-latex gloves to not touch the resin, the silicone rubber is easy to clean but the resin is like glue and smell very hard. You will need a very well ventilated place to use the resin.
-Vaseline to unmould the dongle
-Sand paper very thin, for a best finishing you will need a polish paste and a polish tool for your dremel.
-You could also insert some little pieces in the resin to make it more custom, I've added some little SMD resistors.
Let's go then..
Step 1: Preparing the shuttering
First, make the shape of the USB dongle with the moulding paste.
Then you need to make a shuttering with the lego pieces that cover in height the dongle.
Put the dongle inside and fill the shuttering to the half with the paste.
Make four little spots of paste to make a union of the two parts of the mould.
Cover all, paste and shuttering inner sides with vaseline to unmould easily later
A plastic bag in the table will help to not dirt too much the work area, due the silicon rubber do not glue to it.