If I remember correctly, some forms of potentiation should work, as some of the plugged substance will eventually pass through the liver. So, potentiation methods that focus on the liver enzymes would probably be the most successful. However, most of the potentiation methods are focused on getting the most out of oral use, since it's generally the least effective. Plugging
, obviously, will be more effective than oral right out of the gate.
In addition, I believe I read in one of those monstrous threads on potentiation, that if plugging the substance, it would be helpful to add a pinch (or so) of baking soda to the mix prior to insertion; this adjusts the pH of the mixture and can make it easier for the rectum to absorb.
HTH, and make sure to read the threads on potentiation thoroughly to get information for your friend's friend!
Tell him to be careful & be safe - he can always add more, but he can't take it away if it's too much!