I could only see a crest on the slytherin one http://www.hottopic.com/hottopic/PopCulture/EverythingElse/ComicsAnimeCartoons/Harry-Potter-Slytherin-Crest-Varsity-Girls-Cardigan-186883.jsp and it's a very simple one. It looks like the front crest only the sides cut off. So maybe you could do that.
I'm thinking the measurements would be yours, wouldn't you want that, not what they have? The site says "listed in junior sizes".
The gryffindor one didn't have a sleeve crest.
I hope this helps...