Stitch holders are used for when you're not going to knit those stitches for while but will pick them up later for a different section of a pattern.
If you're knitting a continuous pattern like a blanket, putting some of the stitches on a holder won't really work since those stitches will no longer be connected to the main body of the blanket. It would be in two sections.
You could, if you wanted is use two circulars as if they were two straight needles--put a rubberband or tip holder on the other ends. Even if the tips were a size off, you could knit that section with them and switch back to one size when you get to the point where you are now but at the other end, if that makes any sense.