Limit multiselect choices via formapi?

System

Title says it all...is it possible to limit the amount of choices a user can select (ctrl-click) in a multiselect to a maximum of 2? i am able to alert them if they pick more than 2 using the below code, but this isnt a great solution imo. If this isnt possible am i able to remove selections over 2 automatically? thanks in advance

IWEventRegistry.addItemHandler("/category", "onItemChange", doLimit);

function doLimit()
{
var index = IWDatacapture.getItem("/category").getValue();
var num = index.length;
if (num > 2) {
alert("Do not pick more than 2 literature categories!");
}
}

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