Yes mate, your way is much better okay.
So I managed to do the hard and unlogic (!) way, maybe some people will be interested, let me describe.
first of all it is based on the above method but with some modifications.
The reason why this method doesnt work and during the windows installation windows setup gives an error and refuses to install OS is Windows doesnt allow us to install the OS on one physical drive that has more than 4 partitions.
but unfortunately you will have total 5 partitions after applying above method (some are not visible)
2. Recovery HD
3. Machintosh HD (system drive)
5. DATA Partition (that we are trying to add)
So the key to be successive is to delete
your Recovery HD
before you delete your Recovery HD be sure you backed it up to a usb drive or external HD (In case you need it in the future) because after deleting you cannot re-create it.
to back it up Apple released a little software which you can find here: http://support.apple.com/kb/DL1433
be sure that you backed up (better cloned) your OS drive.
to delete it is very easy 2 minute process as described here http://osxdaily.com/...y-hd-partition/
After deleting, open bootcamp manager follow the steps after second step bootcamp manager will ask for windows installation disc.
Now you will decide the amount of the partitions that you want to dedicate for both OSX and windows.
After ur desicion, at the end of the partitioning you need to close the bootcamp and open disc manager to shrink your OSX drive and create a DATA partition.
Unfortunately After november 2011 update of bootcamp it doesnt allow you to exit the bootcamp manager after the creation of BOOTCAMP partition, and it automatically restarts computer so you need to interrubt this process by force ejecting your windows CD during the manager is in the process of partitioning.
to do this, after determining the partition sizes and clicking okay you will see a progress indicator when you see this, either press eject button or press to force eject button (if you have) near your optical drive bay.
this will eject your windows Disc and makes the bootcamp manager ask for it after repartitioning. ignore it and quit the bootcamp manager.
Go to the disk utility, shrink your OSX partition and by pressing the plus sign create a new DATA partition.
after all this you can use terminal and write "diskutil list" to the terminal window to confirm that you have only 4 drives in ur physical drive.
you can now insert back your windows CD.
Restart ur computer by holding the option key after hearing the chime select windows disc from the selection screen and proceed to the regular windows installation.
when you arrive to the installation disc selection screen select BOOTCAMP drive and click drive options and format it. proceed with the installation.
This is important:
During the installation windows setup restarts your mac totaly 3 times as an installation procedure. on each time you need to hold down the option key after you hear the chime and select your windows boot CD not
the windows HD drive
which is added to the boot disc selection screen.
After installation finishes select your user name password make the regional settings, etc. and you are done.
You have your DATA partion.
I was succesfull with macbook pro late 2011.
if you have difficulties feel free to ask.