Its not a good option. Rather you can try to find a PAM sequence before the stop codon and design the sgRNA and the homology arms accordingly. You can refer Figure2 of the paper(http://www.nature.com/srep/2015/150305/srep08841/full/srep08841.html), wherein they have attempted the same. The figure clearly addresses your question. All the best.

Is not a good idea. you need used a sequence before your stop codon, and also, in the same reading frame. You can use the bleuheron tools (http://blueheronbio.com). It's a really good tool to find your PAM sequence. Regards

Thanks Buys. That was helpful.