REPLY: GIven that the OP was questioning where the correct enforcement spot would be, clearly the correct answer is end of the run.
Now the bigger question of whether an official should be flagging this should be answered with a resounding "NO." Unless the defender picked the receiver up over his head and body-slammed him into the turf, keep the flag in your pocket. After a 'simple' hold of the receiver, the covering official should take a quick look at the play in progress to see if the 'infraction' has any relevance to the play. If he sees that it's a draw play, by all means necessary he should resist the temptation to throw the flag.