You don't need to. Your picons are stored on your harddrive/usb in the picon folder.
When you reflash, you just stick your existing hdd/usb in, and all your picons will be available.
You just need 2 external devices. One for flashing. One for use.
In theory you can store your picons in internal memory and add them to a backup build but then you run the risk of your backup being too large. It has to be under 120mb to enable a flash.