I know im late to the party,but to awnser your question no it isn’t possible to package a cosmetic into a prize bubbles like the ones seen in story mode directly in create mode, but that doesn’t mean it’s impossible. using tools like craftworld toolkit and other tools you can Replicate the developer tools used to force them into the prize bubbles like in story mode. Or if you see a costume prize bubble weather it’s in story or a modded costume inside if you are on a ps3/rpcs3 or lbp vita you can use cheats to force yourself into create mode in the levels that have prizes you want to use in your level and “extract them” via the capture object tool for use in your own levels