Ok so you knit 10 and then slip these onto a holder, the working yarn is coming from the last of these 10 sticthes. Ignore the fact that the working yarn is attached to anything and just continue knitting (in in the bind off stitches) as if the working yarn was coming from a fresh ball of yarn or as if the slipped stitches were still on your right needle.
Put it this way if you where knitting in the round on DPNs and had just knit 10 stitches onto your right DPN and were about to use the empty needle to knit from the left DPN you are basically ‘holding’ the 10 knit stitches on a DPN whilst you carry on working from the left needle. In this case the stitch holder is behaving int he same way as the DPN. the yarn may is coming form it but the stitches are taking no further part in the action.