Get multiple assignables in "one" query.

I am trying to build a report using the API (but am open to other suggestions) of all the test cases in a release with their test steps .

I have all the test cases, but I don't see how to ask for the steps from several test cases at the same time. I know this doesn't work, but I'm hoping it communicates what I'm hoping for.
http://targetprocess/api/v1/Testcases/3,5,17,19,23,29,31,32/testSteps
Where this returns the test steps for test case 3, 5 ,17, 19, 23, 29, 31, and 32.

Basically, I'm hoping to avoid a large number of HTTP calls, but will do them if that's my only option (I can parallelize).