Just sayin':
A long time ago Sony released their custom theme tool. If you go to us.playstation... you will find an out dated version of it that isn't kept up. jp.playstation..., however, has it up to date (6.00) and includes the + cat icon.

Direct Link:
PlayStation.com(Japan) | PSP®—pƒe[ƒ}ƒKƒCƒhƒ‰ƒCƒ“‚¨‚æ‚уe[ƒ}ì¬ƒc[ƒ‹ƒ_ƒEƒ“ƒ[ƒh

I may update this with tutorials or something if I get around to using the tool.