This is an old post, but I though I would add a solution to display the alert just above the clicked button. Of course, you need to include the jQuery.js file on your page for the code below to work. The code will position the radalert just above the button with its left side aligned with left side of button.
pos = $(
win = radalert(
'<span style="font-size:medium;font-weight:bold;">Please input the minimum inventory qauntity.</span>'
, 340, 180,
win.moveTo(pos.left, pos.top - 20 - win.get_height());