lite has made available a Kiosk2Retail PlayStation 3 MFW (Modified Firmware) that allows users to convert their consoles without downgrading for 3.55 Firmware and below.

Download: PS3MFW 3.55 Kiosk2Retail You must login or register to view this content.

To quote:
I joined a PS3 MFW firmeware modified by me, you can use it to convert a PS3 on "Demo / Kiosk Mode" to Retail Mode, you must apply it in Recovery Mode. It will put a vsh update, and definitely get out your ps3 from demo mode to retail.

After that you have the choice to keep the FW on the PS3 and start your backups using the current managers, so the FW is functional.

Or you can call in OFW 3.55 to recover a Waninkoko, rebug or kmeaw...

The FW is in 3.55, patched with "promo-to-retail patch" which will allows you to install it on any PS3 Demo (3.55 and lower).

NB: Patches present on the FW "LV1 HP, LV2 Kernel, Package Installer, UNSigned App Launcher, 2 icones in XMB {App_Home}+{Install Package Files} and patch promo-to-retail". Enjoy.