I took a roll of tie wire and pair of pliers up with me onto the roof and used it to make hooks up and under the tiles. The ridges were more tricky, but ours needed repointing and I just found some gaps and stuffed the hooks in where I could. Left them all in place for the next year.
I ran one set of lights power in under a tile too, it was easier to get the power back to the garage that way as opposed to over the guttering, under the eaves, in the Window. I did have a convenient hole in the ceiling and no sarking to get the line back to the power point though.