After making the sweater to measurements, I decided I would like it 2" longer. (I'm a fairly novice knitter). All my research has pointed me to cutting the cast-on row and ripping back to the body of the sweater.

Because the sweater was knit in 4 pieces (seamed on sides and in middle of front and back), I hate to rip back to the body of the sweater.
The sweater has a simple garter stitch border. Is it possible to pick up and knit in the round to add length? Other ideas? Or should I just take it to my knitting store and beg to pay someone to rip this back for me?