Some people in that thread were wondering whether you need PSN account for this to work, and since I'm too lazy to register there, I'll report here.
1. You DO NOT need PSN account for this (it will work even if your PS3 has never been online).
2. You MUST have the latest firmware installed OR avoid the firmware update requirement on accessing "What's New" section in some other way.
I personally bought a brand new factory sealed Super Slim with firmware 4.22 installed, and was able to get its IDPS after having upgraded it to OFW 4.66 (I don't need ODE compatibility because I already have CFW on another PS3).
The only thing I had to do after updating the firmware was entering country and birth date to access appropriate "What's New" content (default country and "today" as birthday worked fine).
If you have to keep the outdated firmware to use your ODE, I've seen reports of people getting IDPS on 4.5x firmware PS3s by spoofing current firmware version check with another proxy server first, then disabling that proxy and switching to idpstealer proxy to get the IDPS.