You could position a marker span at the end of the selection, get its coordinates using jQuery, place your button at those coordinates and remove the marker span.

The following should get you started:

var markSelection = (function() {

    var markerTextChar = ufeff;

    var markerTextCharEntity = ;



    var markerEl, markerId = sel_ + new Date().getTime() + _ + Math.random().toString().substr(2);



    var selectionEl;



    return function(win) {

        win = win || window;

        var doc = win.document;

        var sel, range;

        // Branch for IE <= 8 

        if (doc.selection && doc.selection.createRange) {

            // Clone the TextRange and collapse

            range = doc.selection.createRange().duplicate();

            range.collapse(false);



            // Create the marker element containing a single invisible character by creating literal HTML and insert it

            range.pasteHTML('<span id=' + markerId + ' style=position: relative;>' + markerTextCharEntity + '</span>');

            markerEl = doc.getElementById(markerId);

        } else if (win.getSelection) {

            sel = win.getSelection();

            range = sel.getRangeAt(0).cloneRange();

            range.collapse(false);



            // Create the marker element containing a single invisible character using DOM methods and insert it

            markerEl = doc.createElement(span);

            markerEl.id = markerId;

            markerEl.appendChild( doc.createTextNode(markerTextChar) );

            range.insertNode(markerEl);

        }



        if (markerEl) {

            // Lazily create element to be placed next to the selection

            if (!selectionEl) {

                selectionEl = doc.createElement(div);

                selectionEl.style.border = solid darkblue 1px;

                selectionEl.style.backgroundColor = lightgoldenrodyellow;

                selectionEl.innerHTML = &lt;- selection;

                selectionEl.style.position = absolute;



                doc.body.appendChild(selectionEl);

            }



            // Find markerEl position http://www.quirksmode.org/js/findpos.html

        var obj = markerEl;

        var left = 0, top = 0;

        do {

            left += obj.offsetLeft;

            top += obj.offsetTop;

        } while (obj = obj.offsetParent);



            // Move the button into place.

            // Substitute your jQuery stuff in here

            selectionEl.style.left = left + px;

            selectionEl.style.top = top + px;



            markerEl.parentNode.removeChild(markerEl);

        }

    };

})();