I've been doing a little research, and it looks like Ryan's method is the only way to actually get an accurate reading for Chloramine.
Here's what I'm looking at:
http://www.ibtbiomed.com/tech_corner/pdf/chlorine.pdf
First I learned that "Chloramine" is actually a name for a category of chemical compounds that includes 1 chlorine molecule bonded with either 1, 2, or 3 ammonia molecules. These three different chloramine compounds all exist at the same time in any given water sample. That's why an ammonia test can't give you a true reading for Chloramine - there is no set ratio of ammonia molecules to chlorine molecules. Although it did say that the most common form of chloramine in treated water is a one to one ratio, so my ammonia test is most likely only slightly underestimating the total chloramine concentration.
Farther down it gives this explanation of how to test for chloramine:
"There is no direct chemical method for measuring
chloramine. Chloramine is indirectly estimated by
calculating from the results of total and free chlorine. Since
total chlorine is the sum of free chlorine and chloramine, the
chloramine therefore is total chlorine less free chlorine."