Undying Flames + Sensei's Top

[DiTAR]

Hi, I was toying with Exploding wurms http://www.wizards.com/default.asp?x=mtgcom/daily/bb56 and got confused:

When Undying Flames Epic triggers at the beginning of the upkeep may I re-order with top in response?

Thanks in advance.

[4-bar-killa]

You can respond to the Epic Trigger or after the Copy goes onto the stack but before it resolves with the Sensei.