Gray out select boxes once max number have been checked

I've got a request on a select question with a lengthy list to gray out unselected boxes once the max number have been checked. It's set to select a minimum of 1 and maximum of 5 options. It's a constructed list with 97 options total where respondents will see either 38 or 59 options total.

Zach, is this something that you could do with some javascript or would it be getting too complex?