Aaaahh! i see i just made a conclusion that as you was knocking down walls and such like you was doing a full resto on the house without time restrictions, well with your preferences then yes a maciator is a good idea but don't forget you only need 4" in height to get the correct minimum fall so depending on your floor height and how low to the ground you could get the t-piece to connect to the existing soil pipe then it could be do able, and don't forget it won't exit the toilet pan at floor level as it's raised slightly for the u-bend.

as for legality's i'm not up to scratch anymore as it's been a long time since i'v done some proper house bashing, i'm sure some searching on the net will bring up some info aswel as some of the people on here more upto scratch with the new reg's and what you can get away with .