yep ...I have gone from copper pipe to compression connection with 3/4" female as this fitting:
http://www.screwfix.com/prods/69498/Plumbing/Compression-Fittings/Conex-FEMALE-IRON-COUPLER-15X3-4
Then screwed the male dog legs 3/4" into the above fitting (these dog legs were supplied with the shower). This is then ready for the shower valve to be screwed on to the other end of the male to male dog leg (but I will fit the dome covers first to ensure the 30mm holes I have cut are fully covered).
http://www.screwfix.com/prods/69498/Plumbing/Compression-Fittings/Conex-FEMALE-IRON-COUPLER-15X3-4
Then screwed the male dog legs 3/4" into the above fitting (these dog legs were supplied with the shower). This is then ready for the shower valve to be screwed on to the other end of the male to male dog leg (but I will fit the dome covers first to ensure the 30mm holes I have cut are fully covered).