unfortunatly you cannot tow with every car. the list used to be very small the ka and smart ect. because these cars were well just too small. many cars however had huge restrictions applied to the towing weights. because of the vehicle design. the more technology that goes into new cars, this list will get bigger looks like yours is one of these.
just to add a little to sprockets answer the legislation governing towing that has come in over the last few years makes some common practice illegal, everything has to be type approved and laid down in the specifications of the vehicle by the manufacturers. these are set in stone and cannot be altered. modifications to these spec's would deem the outfit illegal and would possibly invalidate your insurance and warranty.
the bottom line is, if BMW have not designed that model for towing you cannot tow with it.
in order to tow with any car it has to have the following
1. type approval yours has none.
2. if your car has no approval then the manufacturer deletes the gross train weight from the VIN plate.
3. with no G,T,W, there is no way to establish a max trailer weight. and therefore tow bar manufactures cannot make a type approved bar for it.
4 without a type approved tow bar fitted. you cannot use it to tow with. simple as that really.
even if you did the engine mount modification there is no type approved bar for it,
so this would mean using a bar from a different model that is not Approved. [illegal]
and even if you went ahead and did all this [as reported] the outfit would still be illegal as you have no max trailer weight specification. something VOSA would pick up straight away if you were ever stopped.
and we know where that would lead. heavy fine, points, invalidation of insurance. confiscation of unit ect,ect,
dont do it, just accept this is not a towcar and move on, sorry.