Bingowings said:
Vader's line about it being, "a day long remembered" mitigate much of the threat in the line.
Perhaps you could shave the, "it had better work" or maybe you could replace Vader's over confident line with, "The Emperor is not as forgiving as I am" line from ROTJ suggesting that the gambit is Tarkin's which Vader and the Emperor would punish Tarkin for if it failed.
That's not a bad idea at all. It would just be a matter of making the voice quality more like ANH:R, rather than ROTJ.