Yes, just pick up along the bottom. If you want to add ribbing, it will look like it was originally part of the sweater. If you want to add in st st, then there might be a line, but not too bad, just noticeable. You could use a different color and that would alleviate that problem, too.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog