Now I’ve got a picture in my head.
Either way, you need to attach a new ball of yarn at the sleeves. Whether or not you put the other pieces on extra yarn is up to you. You probably have enough experience at this point to know what’s what and only knit the sleeve stitches, so you could leave them all on the needle and just work the sleeves.
Or at the bottom of the pattern she says this:
**Note. For a totally seamless garment:
Knit across front sts, slip first sleeve sts to a length of spare yarn, cast on 4, knit across back section, slip second sleeve sts to spare yarn, cast on 4, knit across other front. Complete body as given above
This way you put the sleeve stitches on hold and connect the body parts and knit to the bottom. Then you pick up the stitches for the sleeves and work them in the round.