Unfortunately, we don't currently offer a way to customize trackables. We hope to offer custom tracking codes in the future, but we just aren't there yet. However, you can:
Purchase any regular trackable and activate it on Geocaching.com
Use the tracking number for your item — this simply "releases" your item as the actual trackable
Do not release the original trackable into the game — only one tracking code per item, please :-)
So, just purchase the travel bug, but make another tag with the code to go with my item instead of using the trackable bug I buy?