Need Help Explaining This

[Andy]

One of my umpires called me with a situation yesterday and wants to see somthing in the rules that covers this:

ASA rules - Team A is using the DP/FLEX option. In the third inning, DP enters the game on defense as the pitcher, the FLEX is playing another defensive position and the starting pitcher goes to the bench, but is still in the batting order.

DP (pitcher of record) comes up to bat, gets on base, coach requests a Courtesy Runner. I tell my umpire that this is legal.

He insists that the FLEX can only enter on offense for the DP, which is correct, but he is saying that precludes the use of a CR for a DP pitcher. So, he thinks that the only way the DP can be replaced on offense is by the FLEX.

How do I explain it to him, using the rules, that it is OK to have a CR for a DP pitcher?