With the later versions of software on the ES460/470, ERS4500, ERS5500 you can download the software without rebooting the switch.
ES-460#download ?
address Specify IP address of TFTP server
diag Diagnostics image file name
image Software image
image-if-newer Software image if version newer
no-reset do not reset the switch after downloading
poe_module_image PoE image file name
<cr>
You could then reset the switch at your leisure to load the new software.
Cheers!