You must use a java action. There's absolutely no way to retrieve by reference with the reverse flag without a java action. Given your entity/association is named: SomeHelper/SomeHelper_SomeHelper you should write a java action taking the destination object of the reference as a parameter (the so called "child" ) and returning a list of source objects referencing the parameter (the so called "parents", also "association owners").
// BEGIN USER CODE
final boolean reverse = true;
return Core
.retrieveByPath(
getContext(),
child.getMendixObject(),
SomeHelper.MemberNames.SomeHelper_SomeHelper.toString(),
reverse);
// END USER CODE
Hi Yuki,
How are you setting that association in first place? Can you elaborate?