Soil Pipe advice in flying freehold bathroom

[Stevo_Tiler]

Hi,
I'm doing a complete renovation of my bathroom which is a "flying freehold" which means I share the soil pipe with my neighbours. Currently whenever they flush down a trout a little bit of tainted water ens up in my toilet, so after a weekend away I return to a filthy stinking toilet.

Here is an image of the current set up :
http://sphotos.ak.fbcdn.net/hphotos..._414890456072_641516072_4693282_7266806_n.jpghttp://sphotos.ak.fbcdn.net/hphotos..._414890456072_641516072_4693282_7266806_n.jpg

I'd like to install a new hidden cistern Geberit toilet on the right hand wall facing out the same way as the black soil pipe.

Can anyone please advise me on whether this is achievable?
I'm considering chasing out the wall and adding two 45 degree bends to the neighbour's soil pipe and will obviously have to construct boxing for the Geberit toilet on the right hand side wall.

Issues I'd appreciate help on are 1 whether two 45 degree bends in a horizontal soil pipe is advisable & 2 what is the best way to connect the Geberit waste pipe to the existing black soil pipe?

Any ideas and advice very welcome!

Thanks in advance.

Cheers,
Stevo