Do you mean the facebook function, for example, the multiple tab selection function? If so ... there are a number of tutorials on the line for writing your own. The only way that I can imagine that you can "lose weight" is chosen wrong! I took a look at the source, and it seems to me that the “multi select” aspect is pretty clear for the Chosen function. I'm not sure that you will get out of this route.
If you want to write your own, here is a tutorial that you can use to get your desired recording function:
Alternatively, you can check out some other libraries. I found a couple:
“Somewhat large” is a subjective term, but for me, 18k sounds pretty subtle for the smaller version of Chosen. Plus to what I used, and was pleased. However - other libraries abound, so ... happy hunt!