Ok I think I've managed to work this out myself through trial and error - this now works.
I've tweaked my Laravel routing so that the following path will do a '%LIKE%' sql query on anything thrown at it:
http://domain.com/admin/keywords/autocomplete/search/{term}
Using this I modified the ajax call within the tagit plugin to instead just append the input to the end of the url. The final code looks like this:
$("#tags").tagit({
autocomplete: {delay: 0, minLength: 2},
allowSpaces: true,
onlyAvailableTags : false,
tagSource: function(search, showChoices)
{
var that = this;
$.ajax({
url: "/admin/keywords/autocomplete/search/" + search.term,
// data: { term:search.term },
dataType: "json",
success: function(choices)
{
showChoices(that._subtractArray(choices, that.assignedTags()));
}
});
}
});
This does seem to work, and is surprisingly snappy. I know there is likely a better way to do this, however this is the best I could do for now.