I'm pretty sure that there isn't one.

You will probably have to console yourself with War Master's Charge (if you have 9th level maneuvers) which will just get you a free charge attack from all the ghouls within 30' of you but hopefully (if your target is still alive) get the ghouls in position for a full attack on their turn.

I am having trouble working out how many ghouls you can fit within a 30' radius circle but it is quite a lot. Obviously not all of them will get to attack though.

So far my math is: area of a cirlce: pi*radius^2 so pi*(30^2)= 2,827 square feet or 565.4 ghouls? that sounds like way too many but I leave it to better people to work out....

Another approach is using squares, 30' is 6 squares so pi*(6^2) which is 113 squares and thus 113 ghouls... still seems like too many but not quite as badly.