Changing wool start and end of row

I’m knitting a hedgehog which I plan to use as a door stop. The pattern uses two different wools a normal 4 ply and an ‘eye lash’ type of wool for the prickly bits.

I need to cast on 3 stitches in 4 ply, a further 30 in ‘eye lash’ and then a further 3 in 4 ply. This continues throughout the pattern with increases every other row until 106 stitches. Do I carry the 4 ply wool across the back or should I ‘cut off and rejoin’.

It would be better to use intarsia for this critter. There’s a demo under the Free Videos tab at the top of this page, Advanced Techs, Intarsia. You can use another ball of the 4 ply or wind a second ball from the one you have now. With one ball cast on the 3sts, cast on the 30sts eyelash and then use the second ball to cast on the final 3sts in 4 ply. The video shows how to twist strands when you change yarns so that you won’t have a hole. It sems easier to do it this way than to carry the 4 ply all the way across the eyelash sts.
Sounds like a fun project!