You cannot add bubbles on 3.55. Some people install bubbles on lower firmwares and then upgrade, and the bubbles are retained. But since you're already on 3.55, your only option is to replace existing PSP games. For example, say you have ARK installed using the Mimana exploit. You could add a TN-V bubble by downloaded a PSP game/demo (such as "Petz Saddle Club Demo", since it's free), and replace the PBOOT.PBP for that game in PSP/GAME/ with the TN-V PBOOT. This requires that you have a PSP game or demo for every bubble you make, and will continue to use the space of the original game, so it can take up a lot of space to have many bubbles unless all your PSP games are super small.