There are some new transmitters coming out, called RadioPopper, they will be able to transmit the ttl signals via radiowaves, and so they will be less constricted than the Nikon CLS by default. I am not sure when they arrive to shops though.
Have a look here: http://radiopopper.com
It will take some time before these are available in Europe, if ever, as there are mountains of telecoms regulations and approvals that need to be sorted out first.