May be easier if you use the "Paste Special command" rather than manually doing this process multiple times. For the values in the "Paste Special", there is a special trigonometric algorithm for determining what values to set for the rotation and x, y shift. I remember it was up on one of the big surf mapping forums; I'll see if I can find it...
I must say this is brilliant! You can also use this technique to make roads! because the texture rotates along with the brush if you make your rotation small enough you can make a perfect turn!! its really amazing!
You can watch the video and refer back to this tut :D
I didn't really want to post the vid because it was badly done and done in a rush while half-asleep. :P
I thought it might be useful for someone to see it being done though, even with the mistakes.