After a long time without any answer I decide to post my own solution. I doesn't do exactly what I've asked for, but supply readable solution.
It was done with label below the donut, instead of inside donut circle.
Here is working solution on JS Bin
Below You can see a screenshot of working in app:

Here is the code:
JS:
Morris.Donut({
element: 'morrisDonutChart',
data: [
{label: "Download SalesD DDDDDDDDDDDDDDDDD", value: 12},
{label: "In-Store Sales AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", value: 30},
{label: "Mail-Order Sales VVVVVVVVVVVVVVV", value: 20}
]
});
$( "#morrisDonutChart" ).mouseover(function() {
prepareMorrisDonutChart();
});
$( document ).ready(function() {
prepareMorrisDonutChart();
});
function prepareMorrisDonutChart() {
$("#morrisDonutChart tspan:first").css("display","none");
$("#morrisDonutChart tspan:nth-child(1)").css("font-size","40px");
var isi = $("#morrisDonutChart tspan:first").html();
$('#morrisDonutChartSpan').text(isi);
}
HTML head:
<script src="https://ajax.googleapis.com/ajax/libs/mootools/1.5.0/mootools-yui-compressed.js"></script>
<script src="http://cdnjs.cloudflare.com/ajax/libs/raphael/2.1.0/raphael-min.js"></script>
<script src="http://code.jquery.com/jquery-1.8.2.min.js"></script>
<script src="http://cdn.oesmith.co.uk/morris-0.4.1.min.js"></script>
HTML body:
<div id="morrisDonutChart"></div>
<div class="alert alert-info" role="alert">
<span id="morrisDonutChartSpan"></span>
</div>
I hope this will help someone.