Iceland wide angle

Hartblei do exactly what you are talking about

http://www.hartblei.de/en/canon-tse-collar.htm

It looks the business, doing shifts in any direction but it is expensive. RRS does a panoriamic rail and Manfrotto do a cheap one as well

http://www.amazon.co.uk/Manfrotto-454-Micro-Positioning-Plate/dp/B000JLK5QE

But it is a bit fiddly to assemble and only works horizontally.

Mark