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 = "<- 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);
}
};
})();